STATE STREET INSTITUTIONAL INVESTMENT TRUST (Form: 485APOS, Received: 02/25/2010 16:16:06)

As filed with the Securities and Exchange Commission on February 25, 2010

1933 Act File No. 333-30810

1940 Act File No. 811-09819

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 [X]

Post-Effective Amendment No. 31 [X]

and

REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT

OF 1940 [X]

Amendment No. 32 [X]

STATE STREET INSTITUTIONAL INVESTMENT TRUST

P.O. Box 5501, Boston, Massachusetts 02206

(Address of Principal Executive Offices)

(617) 662-1742

(Registrant’s Telephone Number)

David James, Secretary

State Street Bank and Trust Company

4 Copley Place, 5 th floor

Boston, MA 02116

(Name and Address of Agent for Service)

Copy to:

Timothy W. Diggins, Esq.

Ropes & Gray LLP

One International Place

Boston, Massachusetts 02110-2624

It is proposed that this filing will become effective (check appropriate box):

[ ] Immediately upon filing pursuant to paragraph (b)	[ ] On (date) pursuant to paragraph (b)
[ ] 60 days after filing pursuant to paragraph (a)(1)	[X] On April 29, 2010 pursuant to paragraph (a)(1) of Rule 485.
[ ] 75 days after filing pursuant to paragraph (a)(2)	[ ] On (date) pursuant to paragraph (a)(2) of Rule 485.

If appropriate, check the following box:

[ ] This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

State Street Institutional Investment Trust

STATE STREET INSTITUTIONAL LIQUID RESERVES FUND (SSIXX)

STATE STREET INSTITUTIONAL TAX FREE MONEY MARKET FUND (SSTXX)

STATE STREET INSTITUTIONAL U.S. GOVERNMENT MONEY MARKET FUND (GVMXX)

STATE STREET INSTITUTIONAL TREASURY MONEY MARKET FUND (TRIXX)

STATE STREET INSTITUTIONAL TREASURY PLUS MONEY MARKET FUND (TPIXX)

INSTITUTIONAL CLASS

Prospectus Dated April __, 2010

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

AN INVESTMENT IN ANY OF THE FUNDS OFFERED BY THIS PROSPECTUS IS NOT A BANK DEPOSIT AND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY. ALTHOUGH THE FUNDS SEEK TO PRESERVE THE VALUE OF YOUR INVESTMENT AT $1.00 PER SHARE, IT IS POSSIBLE TO LOSE MONEY BY INVESTING IN THE FUNDS.

EACH FUND OFFERS THREE CLASSES OF SHARES: INSTITUTIONAL CLASS, INVESTMENT CLASS AND SERVICE CLASS. THIS PROSPECTUS COVERS ONLY THE INSTITUTIONAL CLASS.

TABLE OF CONTENTS

Fund Summaries	3
State Street Institutional Liquid Reserves Fund	4
State Street Institutional Tax Free Money Market Fund	7
State Street Institutional U.S. Government Money Market Fund	10
State Street Institutional Treasury Money Market Fund	13
State Street Institutional Treasury Plus Money Market Fund	15
Other Information	18
Additional Information About Principal Risks of Investing in the Funds and Portfolios	19
Additional Information About the Funds’ and Portfolios’ Investment Strategies and Risks	21
Management and Organization	25
Shareholder Information	25
Portfolio Holdings Disclosure	25
Payments to Financial Intermediaries	28
Dividends, Distributions and Tax Considerations	28
Financial Highlights	30

Fund Summaries

This section of the Prospectus is composed of a summary description of each Fund. Additional information about each Fund may be found in the other sections of this Prospectus, the first of which begins on page __ of this Prospectus, as well as the Statement of Additional Information dated April __, 2010 applicable to that Fund.

STATE STREET INSTITUTIONAL LIQUID RESERVES FUND

Investment Objective

The investment objective of State Street Institutional Liquid Reserves Fund (the “ILR Fund” or sometimes referred to in context as the “Fund”) is to seek to maximize current income, to the extent consistent with the preservation of capital and liquidity and the maintenance of a stable $1.00 per share net asset value (“NAV”) by investing in U.S. dollar-denominated money market securities. There is no assurance the Fund will be able to maintain a stable NAV per share, and you could lose money by investing in the Fund.

The investment objective of the ILR Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Institutional Class of the ILR Fund. As a shareholder in the State Street Money Market Portfolio (the “Money Market Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees		0.10	%
Other Expenses	__		%
Total Annual Fund Operating Expenses (2)	___		%
Less Reimbursement (2)	___		%
Total Annual Net Operating Expenses (2)	___		%

(1)	Amounts reflect the total expenses of the Money Market Portfolio and the Fund.

(2)	The Adviser has contractually agreed to cap the ILR Fund’s Total Annual Fund Operating Expenses (excluding taxes, interest and extraordinary expenses) attributable to the Institutional Class to the extent that expenses exceed 0.12% of Institutional Class net assets, through April 30, 2011.

Example

This Example is intended to help you compare the cost of investing in the ILR Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, that all dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The ILR Fund invests substantially all of its investable assets in the Money Market Portfolio.

The Money Market Portfolio follows a disciplined investment process in which the Portfolio’s investment adviser bases its decisions on the relative attractiveness of different money market instruments. In the adviser’s opinion, the attractiveness of an instrument may vary depending on the general level of interest rates, as well as imbalances of supply and demand in the market. The Portfolio invests in accordance with regulatory requirements applicable to money market funds, which impose strict conditions on the quality of portfolio securities, the maturity of individual securities and the portfolio as a whole, and portfolio diversification.

The Portfolio attempts to meet its investment objective by investing in a broad range of money market instruments. The Portfolio considers the following instruments or investment strategies to be principal to the achievement of its investment objective: U.S. government securities, including U.S. Treasury bills, notes and bonds and securities issued or guaranteed by U.S. government agencies; certificates of deposits and time deposits of U.S. and foreign banks; commercial paper and other high quality obligations of U.S. or foreign companies; asset-backed securities, including asset-backed commercial paper; and repurchase agreements. These instruments may bear fixed, variable or floating rates of interest or may be zero coupon securities. The Portfolio also may invest in shares of other money market funds, including funds advised by the fund’s investment adviser. Under normal market conditions, the Portfolio intends to invest more than 25% of its total assets in bank obligations.

Principal Investment Risks

An investment in the Fund is not a deposit in a bank and it is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

▪

Risks of Investing Principally in Money Market Instruments:

▪

Interest Rate Risk—The risk that interest rates will rise, causing the value of the Portfolio’s investments to fall. Also, the risk that as interest rates decline, the income that the Portfolio receives on its new investments generally will decline.

▪

Credit Risk—The risk that an issuer, guarantor or liquidity provider of an instrument will fail, including the perception that such an entity will fail, to make scheduled interest or principal payments, which may reduce the Portfolio’s income and the market value of the instrument.

▪

Liquidity Risk—The risk that the Portfolio may not be able to sell some or all of its securities at desired prices, or may be unable to sell the securities at all, because of a lack of demand in the market for such securities, or a liquidity provider defaults on its obligation to purchase the securities when properly tendered by the Portfolio.

▪

Risk Associated with Maintaining a Stable Share Price: To the extent that the aggregate market value of the Portfolio’s assets materially varies from the aggregate of the acquisition prices of those assets, the Fund may not be able to maintain a stable share price of $1.00. This risk typically is higher during periods of rapidly changing interest rates or when issuer credit quality generally is falling, and is made worse when the Portfolio experiences significant redemption requests.

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

Exposure to Financial Institutions: Many instruments in which the Portfolio invests are issued or guaranteed by financial institutions, such as banks and brokers, or are collateralized by securities issued or guaranteed by financial institutions. Changes in the credit worthiness of any of these institutions may adversely affect the value of instruments held by the Portfolio. Adverse developments in the banking industry may cause the Portfolio to underperform other money market funds that invest more broadly across different industries.

•

Repurchase Agreement Risk : If a seller is unable to honor its commitments, the Portfolio could lose money.

▪

Asset-Backed Securities Risk: Defaults on the underlying assets of the asset-backed securities held by the Portfolio may impair the value of the securities, and there may be limitations on the enforceability of any security interest granted with respect to those assets. These securities also present a higher degree of prepayment risk (when repayment of principal occurs before scheduled maturity) and extension risk (when rates of repayment of principal are slower than expected) than do other types of fixed income securities.

▪

Foreign Securities. The Portfolio may invest in U.S. dollar denominated instruments issued by foreign governments, corporations and financial institutions. Financial information relating to foreign issuers may be more limited than financial information generally available for domestic issuers. In addition, the value of instruments of foreign issuers may be adversely affected by local or regional political and economic developments.

▪

Variable and Floating Rate Securities Risk : The extent of increases and decreases in the values of variable and floating rate securities generally will be less than comparable changes in value of an equal principal amount of a similar fixed rate security and, if interest rates decline, the Portfolio may forego the opportunity for price appreciation on the security.

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

The ILR Fund may not achieve its objective and you could lose money by investing in the Fund. An investment in the Fund is not a deposit with a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation (“FDIC”) or any other government agency.

Performance

State Street Institutional Liquid Reserves Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2005:		3.19	%
2006:		5.07	%
2007:		5.28	%
2008:		2.82	%
2009:	___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

Past 1-Year

Past 5-Year

Since the Inception

Date of the Fund

(Annualized)

State Street

Institutional

Liquid Reserves

Fund

______

___

______

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Tax Information

For mutual funds generally, dividends from net investment income (other than qualified dividend income) and distributions of net short-term capital gains are taxable to you as ordinary income under U.S. federal income tax laws whether paid in cash or in additional shares. Distributions from net long-term gains are taxable as long-term taxable gains regardless of the length of time you have held the shares and whether you were paid in cash or additional shares. Dividend and capital gains distributions that you receive, as well as your gains or losses from any sale or exchange of fund shares, may be subject to state and local income taxes.

Purchase and Sale of Fund Shares and Payments to Broker-Dealers and Other Financial Intermediaries

For important information about purchase and sale of Fund shares and financial intermediary compensation, please turn to “Other Information” on page ___ of the prospectus.

STATE STREET INSTITUTIONAL TAX FREE MONEY MARKET FUND

Investment Objective

The investment objective of State Street Institutional Tax Free Money Market Fund (the “Tax Free Fund” or sometimes referred to in context as the “Fund”) is to seek to maximize current income, exempt from federal income taxes, to the extent consistent with the preservation of capital and liquidity and the maintenance of a stable $1.00 per share NAV. There is no assurance the Fund will be able to maintain a stable NAV per share, and you could lose money by investing in the Fund.

The investment objective of the Tax Free Fund as stated above is fundamental, which means that it may not be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Institutional Class of the Tax Free Fund. As a shareholder in the State Street Tax Free Portfolio (the “Tax Free Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees		0.10	%
Other Expenses	___		%
Total Annual Fund Operating Expenses	___		%

(1)	Amounts reflect the total expenses of the Tax Free Portfolio and the Fund.

Example

This Example is intended to help you compare the cost of investing in the Tax Free Fund with the costs of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The Tax Free Fund invests substantially all of its investable assets in the Tax Free Money Market Portfolio.

The Tax Free Portfolio has a fundamental policy of investing at least 80% of its net assets (plus borrowings, if any) in federal tax–exempt, high quality, short-term municipal securities of all types. The Portfolio generally invests all of its assets in instruments exempt from ordinary federal income tax. The Portfolio may not invest more than 20% of its net assets in federally taxable money market instruments, including securities issued by or guaranteed as to principal and interest by the U.S. government or its agencies and instrumentalities, as well as certificates of deposit, commercial paper and repurchase agreements. The Portfolio may buy or sell securities on a when-issued or forward commitment basis.

The Portfolio follows a disciplined investment process that attempts to provide stability of principal, liquidity and current income through all market conditions, by investing in high quality money market instruments. Among other things, the Portfolio’s investment adviser conducts its own credit analyses of potential investments and portfolio holdings, and relies substantially on a dedicated short-term credit research team. In addition, the Portfolio follows regulatory requirements applicable to money market funds. Those requirements are intended to limit the risks of investing in a money market fund by requiring the Portfolio generally to invest in high quality securities with short-term remaining maturities, and be diversified as to issuers, guarantors and other liquidity providers. All securities held by the Portfolio are U.S. dollar-denominated, and they may have fixed, variable or floating interest rates, or may be zero coupon securities. The Portfolio’s weighted average maturity may not exceed 90 days, and is typically much shorter.

The Portfolio attempts to meet its investment objective by investing in, among other things:

•

Securities issues by states, municipalities and their political subdivisions and agencies and certain territories and possessions of the U.S., including:

•

General obligation bonds and notes;

•

Revenue bonds and notes;

•

Commercial paper and other privately issued securities;

•

Tender option bonds;

•

Private activity bonds;

•

Industrial development bonds; and

•

Municipal lease contracts; and

•

Securities of other investment companies with similar investment guidelines.

Principal Investment Risks

In addition, the Fund is subject to the following risks:

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

Risk Associated with Maintaining a Stable Share Price: The ability of the Fund to maintain a stable share price of $1.00 largely depends on the aggregate market value of the Portfolio’s securities being substantially similar to the aggregate of the acquisition prices of those securities to the Portfolio. To the extent that aggregate market value materially varies from the aggregate of those acquisition prices, the Fund may not be able to maintain a stable share price of $1.00. This risk typically is higher during periods of rapidly changing interest rates or issuer credit quality generally is falling, and is made worse when the Portfolio experiences significant redemption requests.

▪

Municipal Obligations Risk: The municipal securities market in which the Portfolio invests may be volatile and may be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities. Municipal revenue obligations are backed by the revenues generated from a specific project or facility and include industrial development bonds and private activity bonds. Private activity and industrial development bonds are dependent on the ability of the facility’s user to meet its financial obligations and the value of any real or personal property pledged as security for such payment. Many municipal securities are issued to finance projects relating to education, health care, transportation and utilities. Conditions in those sectors may affect the overall municipal market. In addition, municipal securities backed by current or anticipated revenues from a specific project or specific asset may be adversely affected by the discontinuance of the taxation supporting the project or asset or the inability to collect revenues for the project or from assets. If any issuer of a municipal security does not comply with applicable tax requirements, or there are adverse changes in federal tax laws, interest paid on the security may become taxable and the security could decline in value.

▪

Exposure to Financial Institutions: Many instruments in which the Portfolio invests are issued or guaranteed as to principal or interest by banks, brokers and other financial institutions, or are collateralized by securities issued or guaranteed by those institutions. Although the Portfolio attempts to invest only with high quality financial institutions, most financial institutions are dependent on other institutions to fulfill their obligations in the financial markets. Events that would adversely affect one financial institution or financial institutions generally also may have an adverse effect on the financial institution in which the Portfolio invests or that serve as counterparties in transactions with the Portfolio. Changes in the credit worthiness of any of these institutions may cause the Portfolio a loss that affects its share price.

▪

Low Short-Term Interest Rates: As short-term interest rates approach 0%, the Portfolio may maintain substantial cash balances. The Portfolio typically does not receive any income from uninvested cash. In addition, if instruments held by the Portfolio pay interest at very low rates, the Portfolio may generate insufficient income to pay its expenses. At such times, the Portfolio may pay some or all of its expenses from Portfolio assets, and generally the Portfolio would not pay a daily dividend.

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

The Tax Free Fund may not achieve its objective and you could lose money by investing in the Fund. An investment in the Fund is not a deposit with a bank and is not insured or guaranteed by the FDIC or any other government agency.

Performance

State Street Institutional Tax Free Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			2.31	%
2009:		___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended _____) and the lowest return for a quarter was ___ % (quarter ended ____ ).

Average Annual Total Returns

For the Periods Ended December 31, 2009

	Past 1-Year			Since the Inception Date of the Fund (Annualized)

State Street Institutional Tax Free Money Market Fund		___	%		_________	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Tax Information

The Fund’s distributions normally consist of exempt-interest dividends, which are generally not taxable to you for Federal income or alternative minimum tax purposes; it is possible that a portion of the exempt-interest dividends will be taxable to you under the Federal alternative minimum tax. It is also possible that a portion of the Fund’s distributions will not qualify as exempt interest dividends; such distributions will generally be taxable to you as ordinary income, unless you are investing through a tax-deferred arrangement, such as a 401(K) plan or an individual retirement account.

Purchase and Sale of Fund Shares and Payments to Broker-Dealers and Other Financial Intermediaries

For important information about purchase and sale of Fund shares and financial intermediary compensation, please turn to “Other Information” on page ___ of the prospectus.

STATE STREET INSTITUTIONAL U.S. GOVERNMENT MONEY MARKET FUND

Investment Objective

The investment objective of State Street Institutional U.S. Government Money Market Fund (the “U.S. Government Fund” or sometimes referred to in context as the “Fund”) is to seek to maximize current income, to the extent consistent with the preservation of capital and liquidity and the maintenance of a stable $1.00 per share NAV. The Fund invests in U.S. government securities and in repurchase agreements collateralized by U.S. government securities. There is no assurance the Fund will be able to maintain a stable NAV per share, and you could lose money by investing in the Fund.

The investment objective of the U.S. Government Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Institutional Class of the U.S. Government Fund. As a shareholder in the State Street U.S. Government Portfolio (the “U.S. Government Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees		0.10	%
Other Expenses	___		%
Total Annual Fund Operating Expenses	___		%
Less Reimbursement (2)	(___		)%
Total Annual Net Operating Expenses (2)	___		%

(1)	Amounts reflect the total expenses of the U.S. Government Portfolio and the Fund.

(2)

The Adviser has contractually agreed to cap the U.S. Government Fund’s Total Annual Fund Operating Expenses (excluding taxes, interest and extraordinary expenses) attributable to the Institutional Class to the extent that expenses exceed 0.12% of Institutional Class net assets, through April 30, 2011.

Example

This Example is intended to help you compare the cost of investing in the U.S. Government Fund with the cost of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The U.S. Government Fund invests substantially all of its investable assets in the U.S. Government Money Market Portfolio.

The U.S. Government Portfolio typically invests at least 80% of its net assets (plus borrowings, if any) in obligations issued or guaranteed as to principal and interest by the U.S. government or its agencies and instrumentalities, as well as repurchase agreements secured by such instruments. The Portfolio will not invest more that 10% of its net assets (taken at current market value) in repurchase agreements maturing in more than seven days.

The Portfolio follows a disciplined investment process that attempts to provide stability of principal, liquidity and current income through all market conditions, by investing in high quality money market instruments. Among other things, the Portfolio’s investment adviser conducts its own credit analyses of potential investments and portfolio holdings, and relies substantially on a dedicated short-term credit research team. In addition, the Portfolio follows regulatory requirements applicable to money market funds. Those requirements are intended to limit the risks of investing in a money market fund by requiring the Portfolio generally to invest in high quality securities with short-term remaining maturities, and be diversified as to issuers, guarantors and other liquidity providers. All securities held by the Portfolio are U.S. dollar-denominated, and they may have fixed, variable or floating interest rates. The Portfolio’s weighted average maturity may not exceed 90 days, and is typically much shorter.

The Portfolio attempts to meet its investment objective by investing in, among other things:

▪

Obligations issued or guaranteed as to principal and interest by the U.S. government or its agencies and instrumentalities, such as the Federal Home Loan Mortgage Corporation and the Federal National Mortgage Association, and U.S. government-sponsored entities such as the Federal Home Loan Bank, which are neither insured no guaranteed by the U.S. Treasury; and

▪

Repurchase agreements collateralized with high quality securities and other assets.

Principal Investment Risks

In addition, the Fund is subject to the following risks:

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

Government Securities Risks: Securities of certain U.S. government agencies and instrumentalities are not guaranteed by the U.S. Treasury, and to the extent the Portfolio owns such securities, it must look principally to the agency or instrumentality issuing or guaranteeing the securities for repayment. Because the Portfolio emphasizes investment in U.S. government securities, and because U.S. government securities generally are perceived as having low risks compared to most other types of investments, the Portfolio’s performance compared to money marked funds that invest principally in other types of money market instruments may be lower.

▪

Significant Exposure to U.S. Government Agencies and Financial Institutions: Although the Portfolio attempts to invest substantially all of its assets in securities issued or guaranteed by U.S. government agencies and high quality instruments issued by financial institutions, events that would adversely affect the market prices of securities issued or guaranteed by one government agency may adversely affect the market price of securities issued or guaranteed by other government agencies. Similarly, events that would affect the market value of instruments issued by one financial institution may adversely affect the market value of instruments issued by similarly situated financial institutions.

•

Repurchase Agreement Risk : If a seller is unable to honor its commitments, the Portfolio could lose money.

▪

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

The U.S. Government Fund may not achieve its objective and you could lose money by investing in the Fund. An investment in the Fund is not a deposit with a bank and is not insured or guaranteed by the FDIC or any other government agency.

Performance

The bar chart and table below provide some indication of the risks of investing in the U.S. Government Fund by illustrating the variability of the Fund’s returns during the years since inception. The Fund’s past performance does not necessarily indicate how the Fund will perform in the future. Please call (877) 521-4083 for the Fund’s current 7-day yield.

State Street Institutional

U.S. Government Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			2.17	%
2009:		___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

	Past 1-Year			Since the Inception Date of the Fund (Annualized)

State Street Institutional U.S. Government Money Market Fund		___	%		_________	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Tax Information

Purchase and Sale of Fund Shares and Payments to Broker-Dealers and Other Financial Intermediaries

For important information about purchase and sale of Fund shares and financial intermediary compensation, please turn to “Other Information” on page ___ of the prospectus.

STATE STREET INSTITUTIONAL TREASURY MONEY MARKET FUND

Investment Objective

The investment objective of State Street Institutional Treasury Money Market Fund (the “Treasury Fund” or sometimes referred to in context as the “Fund”) is to seek a high level of current income consistent with preserving principal and liquidity and the maintenance of a stable $1.00 per share NAV. There is no assurance the Fund will be able to maintain a stable NAV per share, and you could lose money by investing in the Fund.

The investment objective of the Treasury Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Institutional Class of the Treasury Fund. As a shareholder in the State Street Treasury Portfolio (the “Treasury Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees		0.10	%
Other Expenses	___		%
Total Annual Fund Operating Expenses	___		%

(1)	Amounts reflect the total expenses of the Treasury Portfolio and the Fund.

Example

This Example is intended to help you compare the cost of investing in the Treasury Fund with the cost of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The Treasury Fund invests substantially all of its investable assets in the Treasury Money Market Portfolio.

The Treasury Portfolio attempts to meet its investment objective by investing principally in U.S. Treasury bills, notes and bonds (which are direct obligations of the U.S. government) and repurchase agreements backed by such securities. The Portfolio also may invest in shares of other money market funds, including funds advised by the Portfolio’s investment adviser.

The Portfolio follows a disciplined investment process in which the Portfolio’s investment adviser bases its decision on the relative attractiveness of different money market instruments. In the adviser’s opinion, the attractiveness of an instrument may vary depending on the general level of interest rates, as well as imbalances of supply and demand in the market. The Portfolio invests in accordance with regulatory requirements applicable to money market funds, which impose strict conditions on the quality of portfolio securities, the maturity of individual securities and the portfolio as a whole, and portfolio diversification.

Principal Investment Risks

▪

Risks of Investing Principally in Money Market Instruments:

▪

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

The Treasury Fund may not achieve its objective and you could lose money by investing in the Fund. An investment in the Fund is not a deposit with a bank and is not insured or guaranteed by the FDIC or any other government agency.

Performance

The bar chart and table below provide some indication of the risks of investing in the Treasury Fund by illustrating the variability of the Fund’s returns during the years since inception. The Fund’s past performance does not necessarily indicate how the Fund will perform in the future. Please call (877) 521-4083 for the Fund’s current 7-day yield.

State Street Institutional Treasury Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			1.24	%
2009:		___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

	Past 1-Year			Since the Inception Date of the Fund (Annualized)

State Street Institutional Treasury Money Market Fund		___	%		_________	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Tax Information

Purchase and Sale of Fund Shares and Payments to Broker-Dealers and Other Financial Intermediaries

For important information about purchase and sale of Fund shares and financial intermediary compensation, please turn to “Other Information” on page ___ of the prospectus.

STATE STREET INSTITUTIONAL TREASURY PLUS MONEY MARKET FUND

Investment Objective

The investment objective of State Street Institutional Treasury Plus Money Market Fund (the “Treasury Plus Fund” or sometimes referred to in context as the “Fund”) is to seek a high level of current income consistent with preserving principal and liquidity and the maintenance of a stable $1.00 per share NAV. The Fund invests in a portfolio consisting principally of U.S. Treasury securities and repurchase agreements collateralized by such securities. There is no assurance the Fund will be able to maintain a stable NAV per share, and you could lose money by investing in the Fund.

The investment objective of the Treasury Plus Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Institutional Class of the Treasury Plus Fund. As a shareholder in the State Street Treasury Plus Portfolio (the “Treasury Plus Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees		0.10	%
Other Expenses	___		%
Total Annual Fund Operating Expenses	___		%
Less Reimbursement (2)	( ___		)%
Total Annual Net Operating Expenses (2)	___		%

(1)	Amounts reflect the total expenses of the Treasury Plus Portfolio and the Fund.

(2)

The Adviser has contractually agreed to cap the Treasury Plus Fund’s Total Annual Fund Operating Expenses (excluding taxes, interest and extraordinary expenses) attributable to the Institutional Class to the extent that expenses exceed 0.12% of Institutional Class net assets, through April 30, 2011.

Example

This Example is intended to help you compare the cost of investing in the Treasury Plus Fund with the cost of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The Treasury Plus Fund invests substantially all of its investable assets in the Treasury Plus Money Market Portfolio.

The Treasury Plus Portfolio attempts to meet its investment objective by investing, under normal circumstances, at least 80% of its net assets in U.S. Treasury bills, notes and bonds (which are direct obligations of the U.S. government) and repurchase agreements collateralized by these obligations. The Portfolio also may invest in shares of other money market funds, including funds advised by the Portfolio’s investment adviser.

Principal Investment Risks

▪

Risks of Investing Principally in Money Market Instruments:

▪

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

Repurchase Agreement Risk : If a seller is unable to honor its commitments, the Portfolio could lose money.

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

The Treasury Plus Fund may not achieve its objective and you could lose money by investing in the Fund. An investment in the Fund is not a deposit with a bank and is not insured or guaranteed by the FDIC or any other government agency.

Performance

The bar chart and table below provide some indication of the risks of investing in the Treasury Plus Fund by illustrating the variability of the Fund’s returns during the years since inception. The Fund’s past performance does not necessarily indicate how the Fund will perform in the future. Please call (877) 521-4083 for the Fund’s current 7-day yield.

State Street Institutional

Treasury Plus Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			1.55	%
2009:		____		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

	Past 1-Year			Since the Inception Date of the Fund (Annualized)

State Street Institutional Treasury Plus Money Market Fund		___	%		_________	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Tax Information

Purchase and Sale of Fund Shares and Payments to Broker-Dealers and Other Financial Intermediaries

For important information about purchase and sale of Fund shares and financial intermediary compensation, please turn to “Other Information” on page ___ of the prospectus.

Other Information

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	25,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

By Mail:

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone:

For wire transfer instructions, please call (866) 392-0869 between 8 a.m. and 5 p.m. Eastern time. Redemptions by telephone are permitted only if you previously have been authorized for these transactions.

Through Brokers, Banks and Other Financial Intermediaries. If you wish to purchase or redeem Fund shares through a broker, bank or other financial intermediary, please contact that financial intermediary directly. Your financial intermediary may have an earlier cut-off time for the submission of purchase or redemption orders or may be closed at times when the Fund is open.

Payments to Brokers, Banks and Other Financial Intermediaries

If you purchase the Fund through a broker, bank or other financial intermediary, the Fund and its affiliates may pay the intermediary for the sale of Fund shares and related services. These payments may create a conflict of interest by influencing the broker, bank or other intermediary and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial intermediary’s Website for more information.

Additional Information About Principal Risks of Investing in the Funds and Portfolios

Additional information about risks associated with some of the Funds’ and Portfolios’ investment policies and investment strategies is provided below.

•

Banking Industry Risk . If a Portfolio concentrates more than 25% of its assets in bank obligations, adverse developments in the banking industry may have a greater effect on that Portfolio than on a mutual fund that invests more broadly. Banks may be particularly sensitive to certain economic factors such as interest rate changes, adverse developments in the real estate market, fiscal and monetary policy and general economic cycles. Recent instability in the financial markets has heavily influenced the bank obligations of certain financial institutions, resulting in some cases in extreme price volatility and a lack of liquidity. Governments or their agencies may acquire distressed assets from financial institutions and ownership interests in those institutions. The implications of government ownership and disposition of these assets are unclear, and such a program may have positive or negative effects on the liquidity, valuation and performance of certain bank obligations. [ILR Fund]

•

Foreign Investment Risk . A Portfolio may invest in U.S. dollar-denominated obligations issued by non-U.S. issuers. While such instruments may be denominated in U.S. dollars, this does not eliminate the risk inherent in investing in the securities of foreign issuers. Dollar-denominated instruments issued by entities located in foreign countries could lose value as a result of political, financial and economic events in foreign countries. Issuers of these instruments are not necessarily subject to the same regulatory requirements that apply to U.S. banks and corporations, although the information available for dollar-denominated instruments may be subject to the accounting, auditing and financial reporting standards of the U.S. domestic market or exchange on which they are traded, which standards may be more uniform and more exacting than those to which many foreign issuers are subject. Furthermore, by investing in dollar-denominated instruments rather than directly in a foreign issuer’s stock, a Portfolio can avoid currency risks during the settlement period for either purchases or sales. [ILR Fund]

•

Interest Rate Risk . During periods of rising interest rates, a Portfolio’s yield generally is lower than prevailing market rates causing the value of the Portfolio to fall. In periods of falling interest rates, a Portfolio’s yield generally is higher than prevailing market rates, causing the value of the Portfolio to rise. Typically, the more distant the expected cash flow that the Portfolio is to receive from a security, the more sensitive the market price of the security is to movements in interest rates. If a Portfolio owns securities that have variable or floating interest rates, as interest rates fall, the income the Portfolio receives from those securities also will fall. [All Funds]

▪

Credit Risk. Credit risk is the risk that an issuer, guarantor or liquidity provider of a fixed-income security held by a fund may default on its obligation to pay scheduled interest and repay principal. It includes the risk that one or more of the securities will be downgraded by a credit rating agency; generally, lower rated issuers have higher credit risks. Credit risk also includes the risk that an issuer or guarantor of a security, or a bank or other financial institution that has entered into a repurchase agreement with the fund, may default on its payment or repurchase obligation, as the case may be. Credit risk generally is inversely related to credit quality.

▪

Prepayment Risk and Extension Risk. Prepayment risk and extension risk apply primarily to asset-backed and mortgage-backed securities and certain municipal securities.

Prepayment risk is the risk that principal on mortgages or other loan obligations underlying a security may be repaid prior to the stated maturity date. If the Portfolio has purchased a security at a premium, any repayment that is faster than expected reduces the market value of the security and the anticipated yield-to-maturity. Repayment of loans underlying certain securities tends to accelerate during periods of declining interest rates.

Extension risk is the risk that an issuer will exercise its right to repay principal on an obligation held by a Portfolio later than expected. This may happen when there is a rise in interest rates. Under these circumstances, the value of the obligation will decrease, thus preventing the Portfolio from investing expected repayment proceeds in securities paying yields higher than the yields paid by the securities that were expected to be repaid.

•

Liquidity Risk . Adverse market or economic conditions or investor perceptions may result in little or no trading activity in one or more particular securities, thus, making it difficult for a Portfolio holding the securities to determine their values. A Portfolio holding those securities may have to value them at prices that reflect unrealized losses, or if it elects to sell them, it may have to accept lower prices than the prices at which it is then valuing them. The Portfolio also may not be able to sell the securities at any price. [All Funds]

•

Market Risk . The values of the securities in which a Portfolio invests may go up or down in response to the prospects of individual companies and/or general economic conditions. Price changes may be temporary or may last for extended periods. Recent instability in the financial markets has led the U.S. Government to take a number of unprecedented actions designed to support certain financial institutions and segments of the financial markets that have experienced extreme volatility, and in some cases a lack of liquidity. Federal, state, and other governments, their regulatory agencies, or self regulatory organizations may take actions that affect the regulation of the instruments in which the Portfolios invest, or the issuers of such instruments, in ways that are unforeseeable. Legislation or regulation may also change the way in which the Funds and Portfolios themselves are regulated. Such legislation or regulation could limit or preclude a Fund’s or Portfolio’s ability to achieve its investment objective. Governments or their agencies may also acquire distressed assets from financial institutions and ownership interests in those institutions. The implications of government ownership and disposition of these assets are unclear, and such a program may have positive or negative effects on the liquidity, valuation and performance of the Portfolios’ portfolio holdings. Furthermore, volatile financial markets can expose the Portfolios to greater market and liquidity risk and potential difficulty in valuing portfolio instruments held by the Portfolios. [All Funds]

•

Master/Feeder Structure Risk . Unlike traditional mutual funds that invest directly in securities, each of the Funds pursues its objective by investing substantially all of its assets in the Master Portfolio with substantially the same investment objectives, policies and restrictions. The ability of a Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of a Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the corresponding Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio. The Adviser also serves as investment adviser to the Portfolio. Therefore, conflicts may arise as the Adviser fulfills its fiduciary responsibilities to a Fund and its corresponding Portfolio. For example, the Adviser may have an economic incentive to maintain a Fund's investment in the Portfolio at a time when it might otherwise not choose to do so. [All Funds]

•

Money Market Risk . An investment in the Funds is not a deposit of any bank and is not insured or guaranteed by the FDIC or any other government agency. Although the Funds seek to preserve the value of your investment at $1.00 per share, there can be no assurance that they will do so, and it is possible to lose money by investing in the Funds. [All Funds]

•

Mortgage-Backed and Asset-Backed Securities Risk: Mortgage-backed securities, including collateralized mortgage obligations and certain stripped mortgage-backed securities, represent a participation in, or are secured by, mortgage loans. Asset-backed securities are structured like mortgage-backed securities, but instead of mortgage loans or interests in mortgage loans, the underlying assets may include such items as motor vehicle installment sales or installment loan contracts, leases of various types of real and personal property, and receivables from credit card agreements. During periods of falling interest rates, mortgage- and asset- backed securities, which typically provide the issuer with the right to call or prepay the security prior to maturity, may be called or prepaid, which may result in the Portfolio having to reinvest proceeds in other investments at a lower interest rate. During periods of rising interest rates, the average life of mortgage- and asset-backed securities may be extended because of slower-than expected principal payments. This may lock in a below-market interest rate, increase the security’s duration, and reduce the value of the security. As a result, mortgage and asset-backed securities may have less potential for capital appreciation during periods of declining interest rates than other securities of comparable maturities, although they may have a similar risk of decline in market values during periods of rising interest rates. Prepayment rates are difficult to predict and the potential impact of prepayments on the value of a mortgage- or asset-backed security depends on the terms of the instrument and can result in significant volatility. The price of a mortgage- or asset backed security also depends on the credit quality and adequacy of the underlying assets or collateral. Enforcing rights against the underlying assets or collateral may be difficult, or the underlying assets or collateral may be insufficient if the issuer defaults. Subprime mortgage loans, which typically are made to less creditworthy borrowers, have a higher risk of default than conventional mortgage loans. Therefore, mortgage-backed securities backed by subprime mortgage loans may suffer significantly greater declines in value due to defaults. Some mortgage-backed securities are backed by the full faith and credit of the U.S. government (e.g., mortgage-backed securities issued by the Government National Mortgage Association, commonly known as “Ginnie Mae”), while other mortgage-backed securities (e.g., mortgage-backed securities issued by the Federal National Mortgage Association and the Federal Home Loan Mortgage Corporation, commonly known as “Fannie Mae” and “Freddie Mac”), are backed only by the credit of the government entity issuing them. In addition, some mortgage-backed securities are issued by private entities and, as such, are not guaranteed by the U.S. government or any agency or instrumentality of the U.S. government. [ILR Fund]

•

Municipal Obligations Risk . The values of municipal obligations can fluctuate and may be affected by adverse tax, legislative, or political changes, and by financial developments affecting municipal issuers. Because many municipal obligations are issued to finance specific projects, especially those relating to education, health care, housing, utilities, and water and sewer projects, conditions in these sectors can affect the overall municipal market. Payment of municipal obligations may depend on an issuer’s general unrestricted revenues, revenue generated by a specific project or the operator of a project, government appropriations, or aid from other governments. There is greater credit risk if investors can look only to the revenue generated by a project or the operator of the project because of the relatively limited source of revenue. In addition, future changes in federal tax laws or the activity of an issuer may adversely affect the tax-exempt status of municipal obligations, causing interest received and distributed to shareholders by the Portfolio to be taxable and resulting in a significant decline in the values of such municipal obligations. There is generally less public information available for municipal obligations compared to corporate equities or debt securities, and the investment performance of a Portfolio holding municipal obligations may therefore be more dependent on the analytical abilities of the Portfolio’s adviser.

Municipal obligations may also be subject to call risk (a security could be redeemed prior to maturity) and extension risk (a security’s duration could lengthen due to the deceleration of payments). [Tax Free Fund]

•

Repurchase Agreement Risk . A repurchase agreement is an agreement to buy a security from a seller at one price and a simultaneous agreement to sell it back to the original seller at an agreed-upon price. Repurchase agreements may be viewed as loans made by the Portfolio which are collateralized by the securities subject to repurchase. The Portfolio’s investment return on such transactions will depend on the counterparties’ willingness and ability to perform their obligations under the repurchase agreements. If the Portfolio’s counterparty should default on its obligations and the Portfolio is delayed or prevented from recovering the collateral, or if the value of the collateral is insufficient, the Portfolio may realize a loss. [ILR Fund, U.S. Government Fund and Treasury Plus Fund]

•

U.S. Government Sponsored Enterprises Risk . U.S. government securities are securities issued or guaranteed as to the payment of interest or principal by the U.S. government, by an agency or instrumentality of the U.S. government, or by a U.S. government-sponsored entity. Certain U.S. government securities may not be supported as to the payment of principal and interest by the full faith and credit of the U.S. government or the ability to borrow from the U.S. Treasury. Some U.S. government securities may be supported as to the payment of principal and interest only by the credit of the entity issuing or guaranteeing the security. Investments in U.S. government sponsored enterprises may return less than investments in non-government fixed-income securities. [ILR Fund and U.S. Government Fund]

Additional Information about the Funds’ and Portfolios’ Investment Strategies and Risks

The investments described below reflect the Funds’ and Portfolios’ current practices. In addition to the principal risks described above, other risks are described in some of the descriptions of the investments below:

Asset-Backed Securities . Asset-backed securities are securities whose principal and interest payments are collateralized by pools of assets such as auto loans, credit card receivables, leases, installment contracts and personal property. Payments of principal and interest are passed through to holders of the securities and are typically supported by some form of credit enhancement, such as over collateralization, a letter of credit, surety bond, limited guarantee by another entity or by priority to certain of the borrower’s other securities. The degree of credit enhancement varies, generally applying only until exhausted and covering only a fraction of the security’s par value. If the credit enhancement of an asset-backed security held by a Portfolio has been exhausted, and if any required payments of principal and interest are not made with respect to the underlying loans, the Portfolio may experience loss or delay in receiving payment and a decrease in the value of the security.

Like mortgage-backed securities, asset-backed securities are often subject to more rapid repayment than their stated maturity date would indicate as a result of the pass-through of prepayments of principal on the underlying loans. During periods of declining interest rates, prepayment of loans underlying asset-backed securities can be expected to accelerate. A Portfolio’s ability to maintain positions in such securities will be affected by reductions in the principal amount of such securities resulting from prepayments, and its ability to reinvest the returns of principal at comparable yields is subject to generally prevailing interest rates at that time. To the extent that a Portfolio invests in asset-backed securities, the values of such Portfolio’s portfolio securities will vary with changes in market interest rates generally and the differentials in yields among various kinds of asset-backed securities.

Asset-backed securities present certain additional risks that are not presented by mortgage-backed securities because asset-backed securities generally do not have the benefit of a security interest in collateral that is comparable to mortgage assets. Credit card receivables are generally unsecured and the debtors on such receivables are entitled to the protection of a number of state and federal consumer credit laws, many of which give such debtors the right to set-off certain amounts owed on the credit cards, thereby reducing the balance due. Automobile receivables generally are secured, but by automobiles rather than residential real property. Most issuers of automobile receivables permit the loan servicers to retain possession of the underlying obligations. If the servicer were to sell these obligations to another party, there is a risk that the purchaser would acquire an interest superior to that of the holders of the asset backed securities. In addition, because of the large number of vehicles involved in a typical issuance and technical requirements under state laws, the trustee for the holders of the automobile receivables may not have a proper security interest in the underlying automobiles. Therefore, there is the possibility that, in some cases, recoveries on repossessed collateral may not be available to support payments on these securities. [ILR Fund]

ECDs, ETDs and YCDs . ECDs are U.S. dollar-denominated certificates of deposit issued by a bank outside of the United States. ETDs are U.S. dollar-denominated deposits in foreign branches of U.S. banks and foreign banks. YCDs are U.S. dollar-denominated certificates of deposit issued by U.S. branches of foreign banks. These instruments have different risks than those associated with the obligations of domestic banks. The banks issuing these instruments, or their domestic or foreign branches, are not necessarily subject to the same regulatory requirements that apply to U.S. banks operating in the United States. Foreign laws and accounting standards typically are not as strict as they are in the U.S. so there may be fewer restrictions on loan limitations, less frequent examinations and less stringent requirements regarding reserve accounting, auditing, recordkeeping and public reporting requirements. [ILR Fund]

Investment in other Investment Companies . A Portfolio may invest in other money market funds that are registered as investment companies under the Investment Company Act of 1940, as amended (the “1940 Act”), including mutual funds and exchange-traded funds that are sponsored or advised by the Adviser or its affiliates, to the extent permitted by applicable law or SEC exemptive relief. If a Portfolio invests in other money market funds, shareholders of the Fund will bear not only their proportionate share of the expenses described in this Prospectus, but also, indirectly, the similar expenses, including, for example, advisory and administrative fees, of the money market funds in which the Portfolio invests. Shareholders would also be exposed to the risks associated not only with the investments of the Portfolio (indirectly through the Fund’s investment in the Portfolio) but also to the portfolio investments of the money market funds in which the Portfolio invests. [All Funds]

Mortgage-Backed Securities . Mortgage-backed securities, including collateralized mortgage obligations and certain stripped mortgage-backed securities, represent a participation in, or an investment in a pool secured by, mortgage loans. Each mortgage pool underlying mortgage-backed securities consists of mortgage loans evidenced by promissory notes secured by first mortgages or first deeds of trust or other similar security instruments creating a first lien on owner occupied and non-owner occupied one-unit to four unit residential properties, multifamily (i.e., five or more) properties, agricultural properties, commercial properties and mixed use properties (the “Mortgaged Properties”). The Mortgaged Properties may consist of detached individual dwelling units, multifamily dwelling units, individual condominiums, townhouses, duplexes, triplexes, fourplexes, row houses, individual units in planned unit developments and other attached dwelling units. The Mortgaged Properties may also include residential investment properties and second homes.

Types of mortgage-related securities in which a Portfolio may invest include: Government National Mortgage Association (“GNMA”) Certificates (“Ginnie Maes”), Federal Home Loan Mortgage Corporation (“FHLMC”) Mortgage Participation Certificates (“Freddie Macs”), Federal National Mortgage Association (“FNMA”) Guaranteed Mortgage Certificates (“Fannie Maes”) and Commercial Mortgage-Backed Securities (“CMBS”). Mortgage certificates are mortgage-backed securities representing undivided fractional interests in pools of mortgage backed loans. These loans are made by mortgage bankers, commercial banks, savings and loan associations and other lenders. GNMA is authorized to guarantee the timely payment of the principal of an interest on certificates that are based on and backed by a pool of mortgage loans insured by the Federal Housing Administration (FHA Loans), or guaranteed by the Veterans Administration (VA Loans), or by pools of other eligible mortgage loans. In order to meet its obligations under any guaranty, GNMA is authorized to borrow from the United States Treasury in an unlimited amount. Each Fannie Mae is issued and guaranteed by FNMA and represents an undivided interest in a pool of mortgage loans formed by FNMA. The principal activity of FHLMC currently is the purchase of first lien, conventional, residential mortgage loans and participation interests in such mortgage loans and their resale in the form of mortgage securities, primarily Freddie Mac Certificates.

Since September 2008, Fannie Mae and Freddie Mac (together, the “GSEs”) have been placed under the conservatorship of the Federal Housing Finance Agency (“FHFA”). The US Treasury, FHFA and the Federal Reserve have taken the steps to support the conservatorship. No assurance can be given that those initiatives with respect to the debt and mortgage-backed securities issued by the GSEs and acquired by any of the funds will be successful.

Traditional debt investments typically pay a fixed rate of interest until maturity, when the entire principal amount is due. By contrast, payments on mortgage-backed and many asset-backed investments typically include both interest and partial payment of principal. Principal may also be prepaid voluntarily, or as a result of refinancing or foreclosure. A Portfolio may have to invest the proceeds from prepaid investments in other investments with less attractive terms and yields. As a result, these securities may have less potential for capital appreciation during periods of declining interest rates than other securities of comparable maturities, although they may have a similar risk of decline in market value during periods of rising interest rates. Because the prepayment rate generally declines as interest rates rise, an increase in interest rates will likely increase the duration, and thus the volatility, of mortgage-backed and asset-backed securities. In addition to interest rate risk, investments in mortgage-backed securities composed of subprime mortgages may be subject to a higher degree of credit risk, valuation risk and liquidity risk. Duration is a measure of the expected life of a fixed income security that is used to determine the sensitivity of the security's price to changes in interest rates. Unlike the maturity of a fixed income security, which measures only the time until final payment is due, duration takes into account the time until all payments of interest and principal on a security are expected to be made, including how these payments are affected by prepayments and by changes in interest rates.

A Portfolio may gain investment exposure to mortgage-backed investments by entering into agreements with financial institutions to buy the investments at a fixed price at a future date. A Portfolio may or may not take delivery of the investments at the termination date of such an agreement, but will nonetheless be exposed to changes in value of the underlying investments during the term of the agreement. [ILR Fund]

Municipal Securities . Municipal securities may be issued to obtain funds to be used for various public purposes, including general purpose financing for state and local governments, refunding outstanding obligations, and financings for specific projects or public facilities. General obligations are backed by the full faith and credit of the issuer. These securities include, for example, tax anticipation notes, bond anticipation notes and general obligation bonds. Revenue obligations are generally backed by the revenues generated from a specific project or facility and include industrial development bonds and private activity bonds. Private activity and industrial development bonds are dependent on the ability of the facility's user to meet its financial obligations and the value of any real or personal property pledged as security for such payment. Private activity and industrial development bonds, although issued by industrial development authorities, may be backed only by the assets of the non-governmental users, and the user, rather than the municipality, assumes the credit risk. A municipal bond, like a bond issued by a corporation or the U.S. government, obligates the obligor on the bond to pay the bondholder a fixed or variable amount of interest periodically, and to repay the principal value of the bond on a specific maturity date. Municipal notes are short-term instruments which are issued and sold in anticipation of a bond sale, collection of taxes or receipt of other revenues.

Some municipal securities are insured by private insurance companies, while others may be supported by letters of credit furnished by domestic or foreign banks. In determining the credit quality of insured or letter of credit-backed securities, the Adviser reviews the financial condition and creditworthiness of such parties including insurance companies, banks and corporations.

Unlike most other bonds, however, municipal bonds pay interest that is exempt from federal income taxes and, in some cases, also from state and local taxes. Municipal bonds, and municipal bond funds, can therefore be advantageous to investors in higher tax brackets. However, because the interest is tax-exempt, municipal bond yields typically are lower than yields on taxable bonds and bond funds with comparable maturity ranges. [Tax Free Fund]

Section 4(2) Commercial Paper and Rule 144A Securities. A Portfolio may invest in commercial paper issued in reliance on the private placement exemption from registration afforded by Section 4(2) of the Securities Act of 1933, as amended (the ‘‘1933 Act’’). This commercial paper is commonly called ‘‘Section 4(2) paper.’’ A Portfolio may also invest in securities that may be offered and sold only to ‘‘qualified institutional buyers’’ under Rule 144A of the 1933 Act (‘‘Rule 144A securities’’).

Section 4(2) paper is sold to institutional investors who must agree to purchase the paper for investment and not with a view to public distribution. Any resale by the purchaser must be in a transaction exempt from the registration requirements of the 1933 Act. Section 4(2) paper normally is resold to other institutional investors like a Portfolio through or with the assistance of the issuer or investment dealers that make a market in Section 4(2) paper. As a result it suffers from liquidity risk, the risk that the securities may be difficult to value because of the absence of an active market and the risk that it may be sold only after considerable expense and delay, if at all. Rule 144A securities generally must be sold only to other qualified institutional buyers.

Section 4(2) paper and Rule 144A securities will not be considered illiquid for purposes of a Portfolio’s limitation on illiquid securities if the Adviser (pursuant to guidelines adopted by the Board) determines that a liquid trading market exists for the securities in question. There can be no assurance that a liquid trading market will exist at any time for any particular Section 4(2) paper or Rule 144A securities. The Statement of Additional Information (‘‘SAI’’) addresses the Funds’ and Portfolios’ limitation on illiquid securities. [ILR Fund]

Tax Exempt Commercial Paper . Tax exempt commercial paper is a short-term obligation with a stated maturity of 365 days or less. It is typically issued to finance seasonal working capital needs or as short-term financing in anticipation of longer term financing. Each instrument may be backed only by the credit of the issuer or may be backed by some form of credit enhancement, typically in the form of a guarantee by a commercial bank. Commercial paper backed by guarantees of foreign banks may involve additional risk due to the difficulty of obtaining and enforcing judgments against such banks and the generally less restrictive regulations to which such banks are subject. A Portfolio will only invest in commercial paper rated at the time of purchase not less than Prime-1 by Moody's Investors Service, Inc., A-1 by Standard & Poor's Rating Group or F-1 by Fitch Ratings. [Tax Free Fund]

U.S. Government Securities . U.S. Government securities include a variety of securities (including U.S. Treasury bills, notes, and bonds) that differ in their interest rates, maturities, and dates of issue. While securities issued or guaranteed by the U.S. Treasury and some agencies or instrumentalities of the U.S. Government (such as the Government National Mortgage Association) are supported by the full faith and credit of the United States, securities issued or guaranteed by certain other agencies or instrumentalities of the U.S. Government (such as Federal Home Loan Banks) are supported by the right of the issuer to borrow from the U.S. Government, and securities issued or guaranteed by certain other agencies and instrumentalities of the U.S. Government (such as Fannie Mae and Freddie Mac) are supported only by the credit of the issuer itself. Investments in these securities are also subject to interest rate risk and prepayment risk (as described above under "Mortgage-Backed Securities"), and the risk that the value of the securities will fluctuate in response to political, market, or economic developments. [ILR Fund, U.S. Government Fund, Treasury Fund and Treasury Plus Fund]

Variable and Floating Rate Securities . Variable and floating rate securities are instruments issued or guaranteed by entities such as: (1) the U.S. Government, or an agency or instrumentality thereof, (2) corporations, (3) financial institutions, (4) insurance companies, or (5) trusts. A Portfolio may purchase variable and floating rate securities issued or guaranteed by the U.S. government, or an agency or instrumentality thereof. A variable rate security provides for the automatic establishment of a new interest rate on set dates. Variable rate obligations whose interest is readjusted no less frequently than annually will be deemed to have a maturity equal to the period remaining until the next readjustment of the interest rate. A floating rate security provides for the automatic adjustment of its interest rate whenever a specified interest rate changes. Interest rates on these securities are ordinarily tied to, and are a percentage of, a widely recognized interest rate, such as the yield on 90-day U.S. Treasury bills or the prime rate of a specified bank. Generally, changes in interest rates will have a smaller effect on the market value of variable and floating rate securities than on the market value of comparable fixed-income obligations. Thus, investing in variable and floating rate securities generally allows less opportunity for capital appreciation and depreciation than investing in comparable fixed income securities. Securities purchased by a Portfolio may include variable and floating rate instruments, which may have a stated maturity in excess of the Portfolio’s maturity limitations but which will, except for certain U.S. government obligations, permit the Portfolio to demand payment of the principal of the instrument at least once every 13 months upon not more than 30 days’ notice. Variable and floating rate instruments may include variable amount master demand notes that permit the indebtedness thereunder to vary in addition to providing for periodic adjustments in the interest rate. There may be no active secondary market for a particular variable or floating rate instrument. Nevertheless, the periodic readjustments of their interest rates tend to assure that their value to a Portfolio will approximate their par value. Illiquid variable and floating rate instruments (instruments which are not payable upon seven days’ notice and do not have an active trading market) are subject to a Portfolio’s percentage limitations regarding securities that are illiquid or not readily marketable. The Adviser will continuously monitor the creditworthiness of issuers of variable and floating rate instruments in which the Portfolios invest, and their ability to repay principal and interest. Variable and floating rate securities are subject to interest rate and credit/default risk. [ILR Fund, Tax Free Fund and U.S. Government Fund]

Temporary Defensive Positions . From time to time, a Portfolio may take temporary defensive positions in attempting to respond to adverse market, economic or other conditions. Temporary defensive positions may be taken, for example, to preserve capital or if a Portfolio is unable to acquire the types of securities in which it normally invests. Temporary defensive positions may include, but are not limited to, investment in U.S. government securities, repurchase agreements collateralized by such securities, the maintenance of uninvested cash, or investment in cash equivalents. A Portfolio’s holdings in temporary defensive positions may be inconsistent with the Portfolio’s principal investment strategy, and, as a result, the Portfolio may not achieve its investment objective. [All Funds]

Portfolio Holdings Disclosure

The Funds’ portfolio holdings disclosure policy is described in the SAI.

Management and Organization

The Funds and the Portfolios . Each Fund is a separate, diversified series of the State Street Institutional Investment Trust (the “Trust”), which is an open-end management investment company organized as a business trust under the laws of The Commonwealth of Massachusetts.

Each Fund invests as part of a “master-feeder” structure. A Fund will seek to achieve its investment objective by investing substantially all of its investable assets in a separate mutual fund (a “Portfolio”) that has a substantially identical investment objective, investment policies, and risks as the Fund. All discussions about a Fund’s investment objective, policies and risks should be understood to refer also to the investment objectives, policies and risks of the Portfolio.

A Fund can withdraw its investment in a Portfolio if, at any time, the Fund’s Board of Trustees determines that it would be in the best interests of the Fund’s shareholders, or if the investment objectives of the Portfolio changed so that they were inconsistent with the objectives of the Fund. If a Fund withdraws its investment from a Portfolio, the Fund may invest all of its assets in another Portfolio that has the same investment objective as the Fund, the Adviser may directly manage the Fund’s assets, or the Board may take such other action it deems appropriate and in the best interests of shareholders of the Fund, which may include liquidation of the Fund.

The Adviser . State Street Global Advisors (“SSgA”) is the investment management group of State Street Corporation, a publicly held bank holding company, and includes the Adviser, SSgA FM, a wholly-owned subsidiary. SSgA is one of the world’s largest institutional money managers, and uses quantitative and traditional techniques to manage approximately $1.91 trillion as of December 31, 2009 in investment programs and portfolios for institutional and individual investors. SSgA FM, as the investment adviser to the Funds and the Portfolios, is registered with the SEC under the Investment Advisers Act of 1940, as amended. SSgA FM had approximately $168.4 billion in assets under management at December 31, 2009. Each Fund has entered into an investment advisory agreement with the Adviser pursuant to which the Adviser will manage the Fund’s assets directly, for compensation paid at an annual rate of 0.10% of the Fund’s average daily net assets, in the event that the Fund were to cease investing substantially all of its assets in its corresponding portfolio. The Adviser does not receive any fees from a Fund under that agreement so long as the Fund continues to invest substantially all of its assets in the corresponding portfolio or in another investment company. The Adviser may reimburse expenses or waive fees in order to avoid a negative yield. Any such waiver or reimbursement would be voluntary and may be revised or cancelled at any time. There is no guarantee that a Fund will be able to avoid a negative yield. The Adviser places all orders for purchases and sales of the portfolios’ investments.

A summary of the factors considered by the Board of Trustees in connection with the renewals of the investment advisory agreements for the Funds is available in the Funds’ annual report dated December 31, 2009.

The Adviser’s principal address is State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111.

The Administrator and Custodian . State Street Bank and Trust Company (“State Street”), a subsidiary of State Street Corporation, is the administrator and custodian.

The Transfer Agent and Dividend Disbursing Agent . Boston Financial Data Services, Inc. is the transfer agent and dividend disbursing agent.

The Distributor . State Street Global Markets, LLC. serves as the Funds’ distributor (the “Distributor”) pursuant to the Distribution Agreement between the Distributor and the Trust.

Shareholder Information

Determination of Net Asset Value . The Tax Free Fund determines its NAV per share once each business day at 12:00 p.m. Eastern Time (“ET”) or the close of the New York Stock Exchange (the “NYSE”), whichever is earlier. The Treasury Fund determines its NAV per share once each business day at 2:00 p.m. ET or the close of the NYSE, whichever is earlier. Each of the other Funds determines its NAV per share once each business day at 5:00 p.m. ET except for days when the NYSE closes earlier than its regular closing time (the time when a Fund determines its NAV per share is referred to herein as the “Valuation Time”). Pricing does not occur on NYSE holidays. A business day is one on which the NYSE is open for regular trading. Payment for Fund shares must be in Federal Funds (or converted to Federal Funds by the Transfer Agent) by the Fund’s Valuation Time before a purchase order can be accepted. The Federal Reserve is closed on certain holidays on which the NYSE is open. These holidays are Columbus Day and Veteran’s Day. On these holidays, you will not be able to purchase shares by wiring Federal Funds because Federal Funds wiring does not occur on days that the Federal Reserve is closed.

Each of the Funds seeks to maintain a $1.00 per share NAV and, accordingly, uses the amortized cost valuation method to value its portfolio instruments. The amortized cost valuation method initially prices an instrument at its cost and thereafter assumes a constant amortization to maturity of any discount or premium, regardless of the impact of fluctuating interest rates on the market value of the instrument.

If you hold shares of a Fund through a broker-dealer or other financial intermediary, your intermediary may offer additional services and account features that are not described in this Prospectus. Please contact your intermediary directly for an explanation of these services.

Purchasing Shares . Investors pay no sales load to invest in the Institutional Class of the Funds. The price for Fund shares is the NAV per share. Orders will be priced at the NAV next calculated after the order is accepted by the Funds.

Purchase orders in good form and payment received the same day by Fed Wire will receive that day’s NAV and will earn dividends declared on the date of the purchase. All purchases that are made by check will begin earning dividends the following business day after the purchase date.

The minimum initial investment in Institutional Class shares of the Funds is $25 million, although the Adviser may waive the minimum in its discretion. There is no minimum subsequent investment, except in relation to maintaining certain minimum account balances (See “Redeeming Shares” below). The Funds intend to be as fully invested as is practicable; therefore, investments must be made in Federal Funds (i.e., monies credited to the account of the Funds’ custodian bank by a Federal Reserve Bank). The Funds require prior notification of subsequent investments in excess of: $5,000,000 for the Tax Free Fund; $10,000,000 for the Treasury Fund; and $50,000,000 for the ILR Fund, U.S. Government Fund, and Treasury Plus Fund.

The Funds reserve the right to cease accepting investments at any time or to reject any investment order. In addition, the ILR Fund and U.S. Government Fund may limit the amount of a purchase order received after 3:00 p.m. ET. The Treasury Fund and the Treasury Plus Fund may limit the amount of a purchase order received after 1:00 p.m. ET.

How to Purchase Shares

By Mail:

An initial investment in the Funds must be preceded or accompanied by a completed, signed Institutional Account Application Form, sent to:

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone/Fax:

An initial investment in the Funds must be preceded or accompanied by a completed, signed Institutional Account Application Form, faxed to (816) 218-0400. Call the Fund at (866) 392-0869 between the hours of 8:00 a.m. ET and 5:00 p.m. ET to:

Ø confirm receipt of the faxed Institutional Account Application Form (initial purchases only),

Ø request your new account number (initial purchases only),

Ø confirm the amount being wired and wiring bank, and

Ø receive a confirmation number for your purchase order (your trade is not effective until you have received a confirmation number from the Fund).

For your initial investment, send the original, signed Institutional Account Application Form to the address above.

Wire Instructions:

Instruct your bank to transfer money by Federal Funds wire to:

State Street Bank and

Trust Company

2 Avenue de Lafayette

Boston, MA 02111

ABA# 011000028

DDA# 9905-801-8

State Street Institutional Investment Trust ________Fund _______ Class

Account Number

Account Registration

On Columbus Day and Veteran’s Day, you will not be able to purchase shares by wiring Federal Funds because the Federal Funds wiring does not occur on those days. Payment for Fund shares must be in Federal Funds (or converted to Federal Funds by the Transfer Agent) by the Fund’s Valuation Time before a purchase order can be accepted.

You will not be able to redeem shares from the account until the original Application has been received. The Funds and the Funds’ agents are not responsible for transfer errors by the sending or receiving bank and will not be liable for any loss incurred due to a wire transfer not having been received.

In accordance with certain federal regulations, the Trust is required to obtain, verify and record information that identifies each entity that applies to open an account. For this reason, when you open (or change ownership of) an account, the Trust will request certain information, including your name, residential/business address, date of birth (for individuals) and taxpayer identification number or other government identification number and other information that will allow us to identify you which will be used to verify your identity. We may also request to review other identification documents such as driver license, passport or documents showing the existence of the business entity. If you do not provide sufficient information to verify your identity, the Trust will not open an account for you. As required by law, the Trust may employ various procedures, such as comparing your information to fraud databases or requesting additional information and documentation from you, to ensure that the information supplied by you is correct. The Trust reserves the right to reject any purchase for any reason, including failure to provide the Trust with information necessary to confirm your identity as required by law.

Redeeming Shares . An investor may redeem all or any portion of its investment at the NAV next determined after it submits a redemption request, in proper form, to the Funds. Redemption orders are processed at the NAV next determined after a Fund receives a redemption order in good form. If a Fund receives a redemption order prior to its Valuation Time on a business day, the Fund may send payment for redeemed shares on that day. No dividends will be paid on shares that are redeemed and wired the same day. Otherwise, and except as noted below for the ILR Fund, the shares will normally be redeemed, and payment for redeemed shares sent, on the next business day. Dividends will be earned for the trade date of the redemption but not on the date that the wire is sent. Each Fund, other than the ILR Fund, reserves the right to pay for redeemed shares within seven days after receiving a redemption order if, in the judgment of the Adviser, an earlier payment could adversely affect the Fund. For the ILR Fund, shares are redeemed, and payment for redeemed shares sent, no later than the next business day.

The right of any investor to receive payment with respect to any redemption may be suspended or the payment of the redemption proceeds postponed during any period in which the NYSE is closed (other than weekends or holidays) or trading on the NYSE is restricted or, to the extent otherwise permitted by the Investment Company Act of 1940, as amended (the “1940 Act”), if an emergency exists as a result of which disposal by the Fund of securities owned by it is not reasonably practicable or it is not reasonably practicable for the Fund fairly to determine the value of its net assets. In addition, the SEC may by order permit suspension of redemptions for the protection of shareholders of the Funds. Although each Fund attempts to maintain its NAV at $1 per share, there can be no assurance that it will be successful, and there can be no assurance that a shareholder will receive $1 per share upon any redemption.

A request for a partial redemption by an investor whose account balance is below the minimum amount or a request for partial redemption by an investor that would bring the account below the minimum amount may be treated as a request for a complete redemption of the account. These minimums may be different for investments made through certain financial intermediaries as determined by their policies and may be waived in the Adviser’s discretion. The Funds reserve the right to modify minimum account requirements at any time with or without prior notice. The Funds also reserve the right to involuntarily redeem an investor’s account if the investor’s account balance falls below the applicable minimum amount due to transaction activity.

How to Redeem Shares

By Mail

Send a signed letter to:

State Street Institutional Investment Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

The letter should include information necessary to process your request as described below. The Fund may require a medallion guarantee in certain circumstances. See “Medallion Guarantees” below.

By Overnight

State Street Institutional Investment Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone

Please Call (866) 392-0869 between the hours of 8:00 a.m. and 5 p.m. ET.

The Funds will need the following information to process your redemption request:

Ø name(s) of account owners;

Ø account number(s);

Ø the name of the Fund;

Ø your daytime telephone number; and

Ø the dollar amount or number of shares being redeemed.

On any day that the Funds calculate NAV earlier than normal, the Funds reserve the right to adjust the times noted above for purchasing and redeeming shares.

Medallion Guarantees . Certain redemption requests must include a medallion guarantee for each registered account owner if any of the following apply:

Your account address has changed within the last 10 business days.

Redemption proceeds are being transferred to an account with a different registration.

A wire is being sent to a financial institution other than the one that has been established on your Fund account.

Other unusual situations as determined by the Funds’ transfer agent.

All redemption requests regarding shares of the Funds placed after 3:00 p.m. may only be placed by telephone. The Funds reserve the right to postpone payments for redemption requests received after 3:00 p.m. until the next business day. The Funds reserve the right to waive medallion guarantee requirements, require a medallion guarantee under other circumstances or reject or delay redemption if the medallion guarantee is not in good form. Medallion guarantees may be provided by an eligible financial institution such as a commercial bank, a FINRA member firm such as a stock broker, a savings association or a national securities exchange. A notary public cannot provide a medallion guarantee. The Funds reserve the right to reject a medallion guarantee if it is not provided by a STAMP Medallion guarantor.

About Telephone Transactions . Telephone transactions are extremely convenient but are not free from risk. Neither the Funds nor the Funds’ agents will be responsible for any losses resulting from unauthorized telephone transactions if reasonable security procedures are followed. In addition, you are responsible for: (i) verifying the accuracy of all data and information transmitted by telephone, (ii) verifying the accuracy of your account statements immediately upon receipt, and (iii) promptly notifying the Funds of any errors or inaccuracies including, without limitation, any errors or inaccuracies relating to shareholder data or information transmitted by telephone. During periods of heavy market activity or other times, it may be difficult to reach the Funds by telephone. If you are unable to reach us by telephone, consider sending written instructions.

The Funds may terminate the receipt of redemption or exchange orders by telephone at any time, in which case you may redeem or exchange shares by other means.

Policies to Prevent Market Timing . Frequent purchases and redemptions of Fund shares may present risks for other shareholders of the Funds, which may include, among other things, interference in the efficient management of a Fund’s portfolio, dilution in the value of shares held by long-term shareholders, increased brokerage and administrative costs and forcing the Funds to hold excess levels of cash.

The Trust’s Board of Trustees has adopted policies and procedures designed to detect and prevent inappropriate short-term trading activity that is harmful to the Funds. Because most of the shares of the Funds are held by investors indirectly through one or more financial intermediaries, the Funds do not generally have information about the identity of those investors or about transactions effected by those investors. Rather, the Funds and service providers to the Funds periodically review cash inflows and outflows from and to those intermediaries in an attempt to detect inappropriate trading activity by investors holding shares through those intermediaries. The Funds may seek to obtain underlying account trading activity information from financial intermediaries when, in the Adviser’s judgment, the trading activity suggests possible market timing. There is no assurance that the Funds or the Adviser will be able to determine whether trading in the Funds’ shares by an investor holding shares through a financial intermediary is trading activity that may be harmful to the Funds or the Funds’ shareholders.

The Funds reserve the right in their discretion to reject any purchase, in whole or in part, including, without limitation, by a person whose trading activity in Fund shares the Adviser believes could be harmful to the Funds. The Funds may decide to restrict purchase activity in their shares based on various factors, including, without limitation, whether frequent purchase and sale activity will disrupt portfolio management strategies or adversely affect performance. There can be no assurance that the Funds, the Adviser, State Street or their agents will identify all frequent purchase and sale activity affecting the Funds.

Payments to Financial Intermediaries

The Adviser, or an affiliate of the Adviser, out of its own resources, and without additional cost to a Fund or its shareholders, may make additional payments to financial intermediaries (including affiliates of the Adviser) whose clients or customers invest in the Funds. Generally, such financial intermediaries may (though they will not necessarily) provide shareholder servicing and support for their customers who purchase shares of the Funds. Not all financial intermediaries receive additional compensation and the amount of compensation paid varies for each financial intermediary. If payments to financial intermediaries by a particular mutual fund complex’s distributor or adviser exceed payments by other mutual fund complexes, your financial adviser and the financial intermediary employing him or her may have an incentive to recommend that fund complex over others. Please speak with your financial adviser to learn more about the total amounts paid to your financial adviser and his or her firm by the Adviser and its affiliates, and by sponsors of other mutual funds he or she may recommend to you. You should also consult disclosures made by your financial intermediary at the time of purchase.

Dividends, Distributions and Tax Considerations

The Funds intend to declare dividends on shares from net investment income daily and pay them as of the last business day of each month. Distributions from capital gains, if any, will be made annually in December.

The following discussion is a summary of some important U.S. federal tax considerations generally applicable to investments in the Funds. Your investment in the Funds may have other tax implications. Please consult your tax advisor about foreign, federal, state, local or other tax laws applicable to you. Investors, including non-U.S. investors, should consult the SAI tax section for more complete disclosure.

Each Fund intends to elect to be treated and qualify each year as a regulated investment company. A regulated investment company is generally not subject to tax at the corporate level on income and gains that are distributed to shareholders. However, a Fund’s failure to qualify as a regulated investment company would result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

For federal income tax purposes, distributions of investment income (other than "exempt-interest dividends" described below) are generally taxable to you as ordinary income . Taxes on distributions of capital gains generally are determined by how long the Portfolio owned the investments that generated them, rather than how long you have owned your Fund shares. The Funds generally do not expect to make distributions that are eligible for taxation as long-term capital gains.

Distributions from the Tax Free Fund properly designated as "exempt-interest dividends" are not generally subject to federal income tax, including the federal alternative minimum tax for both individual and corporate shareholders, but may be subject to state and local taxes. If you receive Social Security or railroad retirement benefits, you should consult your tax advisor to determine what effect, if any, an investment in the Tax Free Fund may have on the federal taxation of your benefits. Distributions of the Tax Free Fund's income other than exempt-interest dividends generally will be taxable as ordinary income, and distributions of the Tax Free Fund’s net long-term and short-term capital gains (if any) generally will be taxable to you as long-term or short-term capital gain, as applicable, including in respect of gains generated from the sale or other disposition of tax-exempt municipal obligations. The Tax Free Portfolio may also invest a portion of its assets in securities that generate income (that will be allocated to and distributed by the Fund) that will be subject to both federal and state taxes.

Distributions (other than distributions of exempt-interest dividends) are taxable whether you receive them in cash or reinvest them in additional shares. Any gains resulting from the redemption or exchange of Fund shares will generally be taxable to you as either short-term or long-term capital gain, depending upon how long you have held your shares in the Fund.

If you are not a citizen or permanent resident of the United States, each Fund’s ordinary income dividends will generally be subject to a 30% U.S. withholding tax, unless a lower treaty rate applies or unless such income is effectively connected with a U.S. trade or business. A Fund may, under certain circumstances, designate all or a portion of a dividend as an “interest-related dividend” that if received by a nonresident alien or foreign entity generally would be exempt from the 30% U.S. withholding tax, provided that certain other requirements are met. The Funds may also, under certain circumstances, designate all or a portion of a dividend as a “short-term capital gain dividend” which if received by a nonresident alien or foreign entity generally would be exempt from the 30% U.S. withholding tax, unless the foreign person is a nonresident alien individual present in the United States for a period or periods aggregating 183 days or more during the taxable year. The provisions contained in the legislation relating to dividends to foreign persons would apply to dividends with respect to taxable years of a Fund beginning after December 31, 2004 and before January 1, 2010.

Financial Highlights

The Financial Highlights table is intended to help you understand the financial performance of the ILR Fund, the Tax Free Fund, the U.S. Government Fund, the Treasury Fund, and the Treasury Plus Fund, since their inception. Certain information reflects financial results for a single Institutional Class share of each fund. The total return in the table represents the rate that an investor would have earned (or lost) on an investment in Institutional Class shares of each Fund (assuming reinvestment of all dividends and distributions). This information has been audited by ________, whose report, along with each listed Fund’s financial statements, is included in the Funds’ annual report, which is available upon request. The financial information included in this table should be read in conjunction with the financial statements incorporated by reference in the SAI.

For more information about the Funds:

The Funds’ SAI includes additional information about the Funds and is incorporated by reference into this document. Additional information about the Funds’ investments is available in the Funds’ annual and semiannual reports to shareholders.

The SAI and the Funds’ annual and semi-annual reports are available, without charge, upon request. Shareholders in the Funds may make inquiries to the Funds to receive such information by calling State Street Global Markets, LLC at (800) 997-7327 or by writing to the Funds, c/o State Street Global Markets, LLC, State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111-2900. These documents are also available on the Funds’ website at http://www.sttfunds.com.

Information about the Funds (including the SAI) can be reviewed and copied at the Commission’s Public Reference Room in Washington, D.C. Information on the operation of the Public Reference Room may be obtained by calling the Commission at 1-202-942-8090. Reports and other information about the Funds are available free of charge on the EDGAR Database on the Commission’s Internet site at http://www.sec.gov. Copies of this information also may be obtained, after paying a duplicating fee, by electronic request at the following E-mail address: publicinfo@sec.gov, or by writing the Commission’s Public Reference Section, Washington, D.C. 20549-1520.

SSgA FUNDS MANAGEMENT, INC.

STATE STREET FINANCIAL CENTER

ONE LINCOLN STREET

BOSTON, MASSACHUSETTS 02111

The State Street Institutional Investment Trust’s Investment Company Act File Number is 811-09819.

State Street Institutional Investment Trust

STATE STREET INSTITUTIONAL LIQUID RESERVES FUND (SSVXX)

STATE STREET INSTITUTIONAL TAX FREE MONEY MARKET FUND (TFVXX)

STATE STREET INSTITUTIONAL U.S. GOVERNMENT MONEY MARKET FUND (GVVXX)

STATE STREET INSTITUTIONAL TREASURY MONEY MARKET FUND (TRVXX)

STATE STREET INSTITUTIONAL TREASURY PLUS MONEY MARKET FUND (TPVXX)

INVESTMENT CLASS

Prospectus Dated April __, 2010

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

EACH FUND OFFERS THREE CLASSES OF SHARES: INSTITUTIONAL CLASS, INVESTMENT CLASS AND SERVICE CLASS. THIS PROSPECTUS COVERS ONLY THE INVESTMENT CLASS.

TABLE OF CONTENTS

Fund Summaries			3
State Street Institutional Liquid Reserves Fund			4
State Street Institutional Tax Free Money Market Fund			8
State Street Institutional U.S. Government Money Market Fund			11
State Street Institutional Treasury Money Market Fund			14
State Street Institutional Treasury Plus Money Market Fund			17
Additional Information About Principal Risks of Investing in the Funds and Portfolios			20
Additional Information About the Funds’ and Portfolios’ Investment Strategies and Risks			22
Management and Organization			26
Shareholder Information			26
Portfolio Holdings Disclosure			26
Class Expenses and Distribution and Shareholder Servicing Payments			29
Payments to Financial Intermediaries			30
Dividends, Distributions and Tax Considerations			30
Financial Highlights			31

Fund Summaries

STATE STREET INSTITUTIONAL LIQUID RESERVES FUND

Investment Objective

The investment objective of the ILR Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Investment Class of the ILR Fund. As a shareholder in the State Street Money Market Portfolio (the “Money Market Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.10%
Distribution (12b-1) Fees	0.10%
Other Expenses	___ %
-Service Fee	0.25%
Total Annual Fund Operating Expenses	___ %
Less Reimbursement (2)	(___%)
Total Annual Net Operating Expenses (2)	___

(1)

Amounts reflect the total expenses of the Money Market Portfolio and the Fund.

(2)

The Adviser has contractually agreed to cap the ILR Fund’s Total Annual Fund Operating Expenses (excluding taxes, interest and extraordinary expenses) attributable to the Investment Class to the extent that expenses exceed 0.47% of Investment Class net assets, through April 30, 2011.

Example

This Example is intended to help you compare the cost of investing in the ILR Fund with the cost of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

______

Principal Investment Strategies

The ILR Fund invests substantially all of its investable assets in the Money Market Portfolio.

Principal Investment Risks

▪

Risks of Investing Principally in Money Market Instruments:

▪

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

Low Short-Term Interest Rates . As short-term interest rates approach 0%, the Portfolio may maintain substantial cash balances. The Portfolio typically does not receive any income from uninvested cash. In addition, if the Portfolio generates insufficient income to pay its expenses, it may not pay a daily dividend.

▪

•

Repurchase Agreement Risk : If a seller is unable to honor its commitments, the Portfolio could lose money.

▪

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

Performance

The bar chart and table below provide some indication of the risks of investing in the ILR Fund by illustrating the variability of the Fund’s returns during the years since inception. The Fund’s past performance does not necessarily indicate how the Fund will perform in the future. Additionally, the performance information prior to October 1, 2007, the inception date for the Investment Class of the Fund, is that of the Fund before the Investment Class and Institutional Class were operational. The Fund had lower expenses and typically higher returns than the Investment Class. The primary difference in expenses is the lower distribution (12b-1) fee and absence of shareholder servicing plan and associated fees. Please call (877) 521-4083 for the Fund’s current 7-day yield.

State Street Institutional Liquid Reserves Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2005:		3.19	%
2006:		5.07	%
2007:		5.28	%
2008:		2.46	%
2009:	___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____). Additionally, the performance information prior to October 1, 2007, the inception date for the Investment Class of the Fund, is that of the Fund before the Investment Class was operational. The Fund had lower expenses and typically higher returns than the Investment Class. The primary difference in expenses is the lower distribution (12b-1) fee and absence of shareholder servicing plan and associated fees. The Fund’s inception date was August 12, 2004.

Average Annual Total Returns

For the Periods Ended December 31, 2009

Past 1-Year

Past 5-Year

Since the Inception

Date of the Fund

(Annualized)

State Street Institutional

Liquid Reserves Fund

______

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	25,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

By Mail:

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

STATE STREET INSTITUTIONAL TAX FREE MONEY MARKET FUND

Investment Objective

The investment objective of the Tax Free Fund as stated above is fundamental, which means that it may not be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Investment Class of the Tax Free Fund. As a shareholder in the State Street Tax Free Portfolio (the “Tax Free Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees		0.10	%
Distribution (12b-1) Fees		0.10	%
Other Expenses	___		%
-Service Fee		0.25	%
Total Annual Fund Operating Expenses	___		%

(1)

Amounts reflect the total expenses of the Tax Free Portfolio and the Fund.

Example

This Example is intended to help you compare the cost of investing in the Tax Free Fund with the costs of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The Tax Free Fund invests substantially all of its investable assets in the Tax Free Money Market Portfolio.

The Portfolio attempts to meet its investment objective by investing in, among other things:

•

Securities issues by states, municipalities and their political subdivisions and agencies and certain territories and possessions of the U.S., including:

•

General obligation bonds and notes;

•

Revenue bonds and notes;

•

Commercial paper and other privately issued securities;

•

Tender option bonds;

•

Private activity bonds;

•

Industrial development bonds; and

•

Municipal lease contracts; and

•

Securities of other investment companies with similar investment guidelines.

Principal Investment Risks

In addition, the Fund is subject to the following risks:

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

Performance

The bar chart and table below provide some indication of the risks of investing in the Tax Free Fund by illustrating the variability of the Fund’s returns during the years since inception. The Fund’s past performance does not necessarily indicate how the Fund will perform in the future. Additionally, the performance information prior to October 1, 2007, the inception date for the Investment Class of the Fund, is that of the Fund before the Investment Class was operational. The Institutional Class had lower expenses and typically higher returns than the Investment Class. The primary difference in expenses is the lower distribution (12b-1) fee and absence of shareholder servicing plan and associated fees. Please call (877) 521-4083 for the Fund’s current 7-day yield.

State Street Institutional Tax Free Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			1.96	%
2009:		___		%

During the period shown in the bar chart, the highest return for a quarter was___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____). Additionally, the performance information prior to October 1, 2007, the inception date for the Investment Class of the Fund, is that of the Fund before the Investment Class was operational. The Fund had lower expenses and typically higher returns than the Investment Class. The primary difference in expenses is the lower distribution (12b-1) fee and absence of shareholder servicing plan and associated fees. The Fund’s inception date was February 7, 2007.

Average Annual Total Returns

For the Periods Ended December 31, 2009

		Past 1-Year				Since the Inception Date of the Fund (Annualized)
State Street Institutional Tax Free Money Market Fund			______	%			______	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	25,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

By Mail:

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

STATE STREET INSTITUTIONAL U.S. GOVERNMENT MONEY MARKET FUND

Investment Objective

The investment objective of the U.S. Government Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Investment Class of the U.S. Government Fund. As a shareholder in the State Street U.S. Government Portfolio (the “U.S. Government Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.10%
Distribution (12b-1) Fees	0.10%
Other Expenses	___ %
-Service Fee	0.25%
Total Annual Fund Operating Expenses	___ %
Less Reimbursement (2)	(___%)
Total Annual Net Operating Expenses (2)	___%

(1)

Amounts reflect the total expenses of the U.S. Government Portfolio and the Fund.

(2)

The Adviser has contractually agreed to cap the U.S. Government Fund’s Total Annual Fund Operating Expenses (excluding taxes, interest and extraordinary expenses) attributable to the Investment Class to the extent that expenses exceed 0.47% of Investment Class net assets, through April 30, 2011.

Example

This Example is intended to help you compare the cost of investing in the U.S. Government Fund with the cost of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The U.S. Government Fund invests substantially all of its investable assets in the U.S. Government Money Market Portfolio.

The Portfolio follows a disciplined investment process that attempts to provide stability of principal, liquidity and current income through all market conditions, by investing in high quality money market instruments. Among other things, the Portfolio’s investment adviser conducts its own credit analyses of potential investments and portfolio holdings, and relies substantially on a dedicated short-term credit research team. In addition, the Portfolio follows regulatory requirements applicable to money market funds. Those requirements are intended to limit the risks of investing in a money market fund by requiring the Portfolio generally to invest in high quality securities with short-term remaining maturities, and be diversified as to issuers, guarantors and other liquidity providers. All securities held by the Portfolio are U.S. dollar-denominated, and they may have fixed, variable or floating interest rates. The Portfolio’s weighted average maturity may not exceed 90 days, and is typically much shorter.

The Portfolio attempts to meet its investment objective by investing in, among other things:

▪

Repurchase agreements collateralized with high quality securities and other assets.

Principal Investment Risks

In addition, the Fund is subject to the following risks:

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

•

Repurchase Agreement Risk : If a seller is unable to honor its commitments, the Portfolio could lose money.

▪

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

Performance

State Street Institutional

U.S. Government Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			1.81	%
2009:		___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

		Past 1-Year				Since the Inception Date of the Fund (Annualized)
State Street Institutional U.S. Government Money Market Fund			______	%			______	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	25,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

By Mail:

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

STATE STREET INSTITUTIONAL TREASURY MONEY MARKET FUND

Investment Objective

The investment objective of the Treasury Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Investment Class of the Treasury Fund. As a shareholder in the State Street Treasury Portfolio (the “Treasury Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees		0.10	%
Distribution (12b-1) Fees		0.10	%
Other Expenses	___		%
-Service Fee		0.25	%
Total Annual Fund Operating Expenses	___		%

(1)	Amounts reflect the total expenses of the Treasury Portfolio and the Fund.

Example

This Example is intended to help you compare the cost of investing in the Treasury Fund with the cost of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The Treasury Fund invests substantially all of its investable assets in the Treasury Money Market Portfolio.

Principal Investment Risks

▪

Risks of Investing Principally in Money Market Instruments:

▪

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

Performance

State Street Institutional Treasury Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			0.93	%
2009:		___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

		Past 1-Year				Since the Inception Date of the Fund (Annualized)
State Street Institutional Treasury Money Market Fund			______	%			______	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	25,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

By Mail:

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

STATE STREET INSTITUTIONAL TREASURY PLUS MONEY MARKET FUND

Investment Objective

The investment objective of the Treasury Plus Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Investment Class of the Treasury Plus Fund. As a shareholder in the State Street Treasury Plus Portfolio (the “Treasury Plus Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.10%
Distribution (12b-1) Fees	0.10%
Other Expenses	___ %
-Service Fee	0.25%
Total Annual Fund Operating Expenses	___ %
Less Reimbursement (2)	(___%)
Total Annual Net Operating Expenses (2)	___%

(1)

Amounts reflect the total expenses of the Treasury Plus Portfolio and the Fund.

(2)

The Adviser has contractually agreed to cap the Treasury Plus Fund’s Total Annual Fund Operating Expenses (excluding taxes, interest and extraordinary expenses) attributable to the Investment Class to the extent that expenses exceed 0.47% of Investment Class net assets, through April 30, 2011.

Example

This Example is intended to help you compare the cost of investing in the Treasury Plus Fund with the cost of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

$_____

_____

Principal Investment Strategies

The Treasury Plus Fund invests substantially all of its investable assets in the Treasury Plus Money Market Portfolio.

Principal Investment Risks

▪

Risks of Investing Principally in Money Market Instruments:

▪

•	Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

▪	Repurchase Agreement Risk : If a seller is unable to honor its commitments, the Portfolio could lose money.

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

Performance

State Street Institutional

Treasury Plus Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			1.27	%
2009:		___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

		Past 1-Year			Since the Inception Date of the Fund (Annualized)
State Street Institutional Treasury Plus Money Market Fund		______	%		______	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	25,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

By Mail:

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

Additional Information About Principal Risks of Investing in the Funds and Portfolios

Additional information about risks associated with some of the Funds’ and Portfolios’ investment policies and investment strategies is provided below.

•

Banking Industry Risk. If a Portfolio concentrates more than 25% of its assets in bank obligations, adverse developments in the banking industry may have a greater effect on that Portfolio than on a mutual fund that invests more broadly. Banks may be particularly sensitive to certain economic factors such as interest rate changes, adverse developments in the real estate market, fiscal and monetary policy and general economic cycles. Recent instability in the financial markets has heavily influenced the bank obligations of certain financial institutions, resulting in some cases in extreme price volatility and a lack of liquidity. Governments or their agencies may acquire distressed assets from financial institutions and ownership interests in those institutions. The implications of government ownership and disposition of these assets are unclear, and such a program may have positive or negative effects on the liquidity, valuation and performance of certain bank obligations. [ILR Fund]

•

▪

Prepayment Risk and Extension Risk. Prepayment risk and extension risk apply primarily to asset-backed and mortgage-backed securities and certain municipal securities.

•

Liquidity Risk. Adverse market or economic conditions or investor perceptions may result in little or no trading activity in one or more particular securities, thus, making it difficult for a Portfolio holding the securities to determine their values. A Portfolio holding those securities may have to value them at prices that reflect unrealized losses, or if it elects to sell them, it may have to accept lower prices than the prices at which it is then valuing them. The Portfolio also may not be able to sell the securities at any price. [All Funds]

•

Master/Feeder Structure Risk. Unlike traditional mutual funds that invest directly in securities, each of the Funds pursues its objective by investing substantially all of its assets in the Master Portfolio with substantially the same investment objectives, policies and restrictions. The ability of a Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of a Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the corresponding Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio. The Adviser also serves as investment adviser to the Portfolio. Therefore, conflicts may arise as the Adviser fulfills its fiduciary responsibilities to a Fund and its corresponding Portfolio. For example, the Adviser may have an economic incentive to maintain a Fund's investment in the Portfolio at a time when it might otherwise not choose to do so. [All Funds]

•

Money Market Risk. An investment in the Funds is not a deposit of any bank and is not insured or guaranteed by the FDIC or any other government agency. Although the Funds seek to preserve the value of your investment at $1.00 per share, there can be no assurance that they will do so, and it is possible to lose money by investing in the Funds. [All Funds]

•

Municipal Obligations Risk. The values of municipal obligations can fluctuate and may be affected by adverse tax, legislative, or political changes, and by financial developments affecting municipal issuers. Because many municipal obligations are issued to finance specific projects, especially those relating to education, health care, housing, utilities, and water and sewer projects, conditions in these sectors can affect the overall municipal market. Payment of municipal obligations may depend on an issuer’s general unrestricted revenues, revenue generated by a specific project or the operator of a project, government appropriations, or aid from other governments. There is greater credit risk if investors can look only to the revenue generated by a project or the operator of the project because of the relatively limited source of revenue. In addition, future changes in federal tax laws or the activity of an issuer may adversely affect the tax-exempt status of municipal obligations, causing interest received and distributed to shareholders by the Portfolio to be taxable and resulting in a significant decline in the values of such municipal obligations. There is generally less public information available for municipal obligations compared to corporate equities or debt securities, and the investment performance of a Portfolio holding municipal obligations may therefore be more dependent on the analytical abilities of the Portfolio’s adviser.

•

Repurchase Agreement Risk. A repurchase agreement is an agreement to buy a security from a seller at one price and a simultaneous agreement to sell it back to the original seller at an agreed-upon price. Repurchase agreements may be viewed as loans made by the Portfolio which are collateralized by the securities subject to repurchase. The Portfolio’s investment return on such transactions will depend on the counterparties’ willingness and ability to perform their obligations under the repurchase agreements. If the Portfolio’s counterparty should default on its obligations and the Portfolio is delayed or prevented from recovering the collateral, or if the value of the collateral is insufficient, the Portfolio may realize a loss. [ILR Fund, U.S. Government Fund and Treasury Plus Fund]

•

U.S. Government Sponsored Enterprises Risk. U.S. government securities are securities issued or guaranteed as to the payment of interest or principal by the U.S. government, by an agency or instrumentality of the U.S. government, or by a U.S. government-sponsored entity. Certain U.S. government securities may not be supported as to the payment of principal and interest by the full faith and credit of the U.S. government or the ability to borrow from the U.S. Treasury. Some U.S. government securities may be supported as to the payment of principal and interest only by the credit of the entity issuing or guaranteeing the security. Investments in U.S. government sponsored enterprises may return less than investments in non-government fixed-income securities. [ILR Fund and U.S. Government Fund]

Additional Information about the Funds’ and Portfolios’ Investment Strategies and Risks

Section 4(2) Commercial Paper and Rule 144A Securities . A Portfolio may invest in commercial paper issued in reliance on the private placement exemption from registration afforded by Section 4(2) of the Securities Act of 1933, as amended (the ‘‘1933 Act’’). This commercial paper is commonly called ‘‘Section 4(2) paper.’’ A Portfolio may also invest in securities that may be offered and sold only to ‘‘qualified institutional buyers’’ under Rule 144A of the 1933 Act (‘‘Rule 144A securities’’).

Variable and Floating Rate Securities. Variable and floating rate securities are instruments issued or guaranteed by entities such as: (1) the U.S. Government, or an agency or instrumentality thereof, (2) corporations, (3) financial institutions, (4) insurance companies, or (5) trusts. A Portfolio may purchase variable and floating rate securities issued or guaranteed by the U.S. government, or an agency or instrumentality thereof. A variable rate security provides for the automatic establishment of a new interest rate on set dates. Variable rate obligations whose interest is readjusted no less frequently than annually will be deemed to have a maturity equal to the period remaining until the next readjustment of the interest rate. A floating rate security provides for the automatic adjustment of its interest rate whenever a specified interest rate changes. Interest rates on these securities are ordinarily tied to, and are a percentage of, a widely recognized interest rate, such as the yield on 90-day U.S. Treasury bills or the prime rate of a specified bank. Generally, changes in interest rates will have a smaller effect on the market value of variable and floating rate securities than on the market value of comparable fixed-income obligations. Thus, investing in variable and floating rate securities generally allows less opportunity for capital appreciation and depreciation than investing in comparable fixed income securities. Securities purchased by a Portfolio may include variable and floating rate instruments, which may have a stated maturity in excess of the Portfolio’s maturity limitations but which will, except for certain U.S. government obligations, permit the Portfolio to demand payment of the principal of the instrument at least once every 13 months upon not more than 30 days’ notice. Variable and floating rate instruments may include variable amount master demand notes that permit the indebtedness thereunder to vary in addition to providing for periodic adjustments in the interest rate. There may be no active secondary market for a particular variable or floating rate instrument. Nevertheless, the periodic readjustments of their interest rates tend to assure that their value to a Portfolio will approximate their par value. Illiquid variable and floating rate instruments (instruments which are not payable upon seven days’ notice and do not have an active trading market) are subject to a Portfolio’s percentage limitations regarding securities that are illiquid or not readily marketable. The Adviser will continuously monitor the creditworthiness of issuers of variable and floating rate instruments in which the Portfolios invest, and their ability to repay principal and interest. Variable and floating rate securities are subject to interest rate and credit/default risk. [ILR Fund, Tax Free Fund and U.S. Government Fund]

Portfolio Holdings Disclosure

The Funds’ portfolio holdings disclosure policy is described in the SAI.

Management and Organization

The Adviser’s principal address is State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111.

The Administrator and Custodian . State Street Bank and Trust Company (“State Street”), a subsidiary of State Street Corporation, is the administrator and custodian.

The Transfer Agent and Dividend Disbursing Agent . Boston Financial Data Services, Inc. is the transfer agent and dividend disbursing agent.

The Distributor . State Street Global Markets, LLC serves as the Funds’ distributor (the “Distributor”) pursuant to the Distribution Agreement between the Distributor and the Trust.

Shareholder Information

Purchasing Shares . The price for Fund shares is the NAV per share. Orders will be priced at the NAV next calculated after the order is accepted by the Funds.

The minimum initial investment in Investment Class shares of the Funds is $25 million, although the Adviser may waive the minimum in its discretion. There is no minimum subsequent investment, except in relation to maintaining certain minimum account balances (See “Redeeming Shares” below). The Funds intend to be as fully invested as is practicable; therefore, investments must be made in Federal Funds (i.e., monies credited to the account of the Funds’ custodian bank by a Federal Reserve Bank). The Funds require prior notification of subsequent investments in excess of: $5,000,000 for the Tax Free Fund; $10,000,000 for the Treasury Fund; and $50,000,000 for the ILR Fund, U.S. Government Fund, and Treasury Plus Fund.

How to Purchase Shares

By Mail:

An initial investment in the Funds must be preceded or accompanied by a completed, signed Institutional Account Application Form, sent to:

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone/Fax:

Ø confirm receipt of the faxed Institutional Account Application Form (initial purchases only),

Ø request your new account number (initial purchases only),

Ø confirm the amount being wired and wiring bank, and

Ø receive a confirmation number for your purchase order (your trade is not effective until you have received a confirmation number from the Fund).

For your initial investment, send the original, signed Institutional Account Application Form to the address above.

Wire Instructions:

Instruct your bank to transfer money by Federal Funds wire to:

State Street Bank and

Trust Company

2 Avenue de Lafayette

Boston, MA 02111

ABA# 011000028

DDA# 9905-801-8

State Street Institutional Investment Trust ________Fund _______ Class

Account Number

Account Registration

How to Redeem Shares

By Mail

Send a signed letter to:

State Street Institutional Investment Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

The letter should include information necessary to process your request as described below. The Fund may require a medallion guarantee in certain circumstances. See “Medallion Guarantees” below.

By Overnight

State Street Institutional Investment Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone

Please Call (866) 392-0869 between the hours of 8:00 a.m. and 5 p.m. ET.

The Funds will need the following information to process your redemption request:

Ø name(s) of account owners;

Ø account number(s);

Ø the name of the Fund;

Ø your daytime telephone number; and

Ø the dollar amount or number of shares being redeemed.

On any day that the Funds calculate NAV earlier than normal, the Funds reserve the right to adjust the times noted above for purchasing and redeeming shares.

Medallion Guarantees . Certain redemption requests must include a medallion guarantee for each registered account owner if any of the following apply:

Your account address has changed within the last 10 business days.

Redemption proceeds are being transferred to an account with a different registration.

A wire is being sent to a financial institution other than the one that has been established on your Fund account.

Other unusual situations as determined by the Funds’ transfer agent.

The Funds may terminate the receipt of redemption or exchange orders by telephone at any time, in which case you may redeem or exchange shares by other means.

Class Expenses and Distribution and Shareholder Servicing Payments

To compensate the Distributor for the services it provides and for the expenses it bears in connection with the distribution of Investment Class shares of the Funds, each Fund makes payments, from the assets attributable to its Investment Class shares, to the Distributor under a distribution plan adopted pursuant to Rule 12b-1 under the 1940 Act (the “Plan”). The Plan is a compensation plan that provides for payments at annual rates (based on average daily net assets) of up to 0.10% of a Fund’s net assets attributable to its Investment Class shares. Because Rule 12b-1 fees are paid out of the Funds’ Investment Class assets on an ongoing basis, they will increase the cost of your investment and may cost you more than paying other types of sales charges. All Investment Class shareholders share in the expense of Rule 12b-1 fees paid by the Funds. It is expected that the Distributor will pay substantially all of the amounts it receives under the Plan to intermediaries involved in the sale of Investment Class shares of the Funds.

The Funds’ Investment Class shares generally are sold to clients of financial intermediaries (“Service Organizations”), including affiliates of the Adviser, which have entered into shareholder servicing agreements with the Funds or Distributor. Service Organizations agree to perform certain shareholder servicing, administrative and accounting services for their clients and customers who are beneficial owners of shares of the Funds. The Funds will make payments to Service Organizations for services provided at an annual rate of up to 0.25% of a Fund’s net assets. The Funds expect to reimburse the Distributor for any such payments made by the Distributor to Service Organizations.

Payments to Financial Intermediaries

Dividends, Distributions and Tax Considerations

For federal income tax purposes, distributions of investment income (other than "exempt-interest dividends" described below) are generally taxable to you as ordinary income. Taxes on distributions of capital gains generally are determined by how long the Portfolio owned the investments that generated them, rather than how long you have owned your Fund shares. The Funds generally do not expect to make distributions that are eligible for taxation as long-term capital gains.

Financial Highlights

The Financial Highlights table is intended to help you understand the financial performance of the ILR Fund, the Tax Free Fund, the U.S. Government Fund, the Treasury Fund, and the Treasury Plus Fund, since their inception. Certain information reflects financial results for a single Investment Class share of each fund. The total return in the table represents the rate that an investor would have earned (or lost) on an investment in Investment Class shares of each Fund (assuming reinvestment of all dividends and distributions). This information has been audited by __________, whose report, along with each listed Fund’s financial statements, is included in the Funds’ annual report, which is available upon request. The financial information included in this table should be read in conjunction with the financial statements incorporated by reference in the SAI.

For more information about the Funds :

SSgA FUNDS MANAGEMENT, INC.

STATE STREET FINANCIAL CENTER

ONE LINCOLN STREET

BOSTON, MASSACHUSETTS 02111

The State Street Institutional Investment Trust’s Investment Company Act File Number is 811-09819.

State Street Institutional Investment Trust

STATE STREET INSTITUTIONAL LIQUID RESERVES FUND (LRSXX)

STATE STREET INSTITUTIONAL TAX FREE MONEY MARKET FUND (TASXX)

STATE STREET INSTITUTIONAL U.S. GOVERNMENT MONEY MARKET FUND (GVSXX)

STATE STREET INSTITUTIONAL TREASURY MONEY MARKET FUND (TYSXX)

STATE STREET INSTITUTIONAL TREASURY PLUS MONEY MARKET FUND (TPSXX)

SERVICE CLASS

Prospectus Dated April __, 2010

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

EACH FUND OFFERS THREE CLASSES OF SHARES: INSTITUTIONAL CLASS, INVESTMENT CLASS AND SERVICE CLASS. THIS PROSPECTUS COVERS ONLY THE SERVICE CLASS.

TABLE OF CONTENTS

Fund Summaries	3
State Street Institutional Liquid Reserves Fund	4
State Street Institutional Tax Free Money Market Fund	7
State Street Institutional U.S. Government Money Market Fund	10
State Street Institutional Treasury Money Market Fund	13
State Street Institutional Treasury Plus Money Market Fund	16
Additional Information About Principal Risks of Investing in the Funds and Portfolios	19
Additional Information About the Funds’ and Portfolios’ Investment Strategies and Risks	21
Management and Organization	25
Shareholder Information	25
Portfolio Holdings Disclosure	25
Shareholder Servicing Payments	28
Payments to Financial Intermediaries	28
Dividends, Distributions and Tax Considerations	29

Fund Summaries

STATE STREET INSTITUTIONAL LIQUID RESERVES FUND

Investment Objective

The investment objective of State Street Institutional Liquid Reserves Fund (the “ILR Fund” or sometimes referred to in context as the “Fund”) is to seek to maximize current income, to the extent consistent with the preservation of capital and liquidity and the maintenance of a stable $1.00 per share net asset value (“NAV”). The Fund invests in U.S. dollar-denominated money market securities. There is no assurance the Fund will be able to maintain a stable NAV per share, and you could lose money by investing in the Fund.

The investment objective of the ILR Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Service Class of the ILR Fund. As a shareholder in the State Street Money Market Portfolio (the “Money Market Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees		0.10	%
Other Expenses	___		%
-Service Fee		0.05	%
Total Annual Fund Operating Expenses	___		%

(1)

Amounts reflect the total expenses of the Money Market Portfolio and the Fund.

Example

This Example is intended to help you compare the cost of investing in the ILR Fund with the cost of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The ILR Fund invests substantially all of its investable assets in the Money Market Portfolio.

Principal Investment Risks

▪

Risks of Investing Principally in Money Market Instruments:

▪

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

•

Repurchase Agreement Risk : If a seller is unable to honor its commitments, the Portfolio could lose money.

▪

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

Performance

The bar chart and table below provide some indication of the risks of investing in the ILR Fund (as represented by the performance of the Fund’s Institutional Class) by illustrating the variability of the Fund’s returns during the years since inception. The Fund’s past performance does not necessarily indicate how the Fund will perform in the future. Performance history will be available for the Service Class of the Fund after it has been in operation for one calendar year. The Institutional Class has lower expenses and higher expected returns than the Service Class. The primary difference in expenses is that the Institutional Class does not bear shareholder servicing fees. Please call (877) 521-4083 for the Fund’s current 7-day yield.

State Street Institutional Liquid Reserves Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2005:		3.19	%
2006:		5.07	%
2007:		5.28	%
2008:		2.82	%
2009:	___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended ____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

Past 1-Year

Past 5-Year

Since the Inception

Date of the Fund

(Annualized)

State Street Institutional

Liquid Reserves Fund-

Institutional Class

___

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	10,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

By Mail :

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

STATE STREET INSTITUTIONAL TAX FREE MONEY MARKET FUND

Investment Objective

The investment objective of the Tax Free Fund as stated above is fundamental, which means that it may not be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Service Class of the Tax Free Fund. As a shareholder in the State Street Tax Free Portfolio (the “Tax Free Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.10%
Other Expenses	0.14 %
-Service Fee	0.05%
Total Annual Fund Operating Expenses	___ %

(1)	Amounts reflect the total expenses of the Tax Free Portfolio and the Fund.

Example

This Example is intended to help you compare the cost of investing in the Tax Free Fund with the costs of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The Tax Free Fund invests substantially all of its investable assets in the Tax Free Money Market Portfolio.

The Portfolio attempts to meet its investment objective by investing in, among other things:

•

Securities issues by states, municipalities and their political subdivisions and agencies and certain territories and possessions of the U.S., including:

•

General obligation bonds and notes;

•

Revenue bonds and notes;

•

Commercial paper and other privately issued securities;

•

Tender option bonds;

•

Private activity bonds;

•

Industrial development bonds; and

•

Municipal lease contracts; and

•

Securities of other investment companies with similar investment guidelines.

Principal Investment Risks

In addition, the Fund is subject to the following risks:

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

Performance

The bar chart and table below provide some indication of the risks of investing in the Tax Free Fund (as represented by the performance of the Fund’s Institutional Class) by illustrating the variability of the Fund’s returns during the years since inception. The Fund’s past performance does not necessarily indicate how the Fund will perform in the future. Performance history will be available for the Service Class of the Fund after it has been in operation for one calendar year. The Institutional Class has lower expenses and higher expected returns than the Service Class. The primary difference in expenses is that the Institutional Class does not bear shareholder servicing fees. Please call (877) 521-4083 for the Fund’s current 7-day yield.

State Street Institutional Tax Free Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			2.31	%
2009:		___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

		Past 1-Year				Since the Inception Date of the Fund (Annualized)
State Street Institutional Tax Free Money Market Fund- Institutional Class			___	%			___	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	10,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

By Mail :

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

STATE STREET INSTITUTIONAL U.S. GOVERNMENT MONEY MARKET FUND

Investment Objective

The investment objective of the U.S. Government Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Service Class of the U.S. Government Fund. As a shareholder in the State Street U.S. Government Portfolio (the “U.S. Government Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.10%
Other Expenses	___ %
-Service Fee	0.05%
Total Annual Fund Operating Expenses	___ %

(1)	Amounts reflect the total expenses of the U.S. Government Portfolio and the Fund.

Example

This Example is intended to help you compare the cost of investing in the U.S. Government Fund with the cost of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The U.S. Government Fund invests substantially all of its investable assets in the U.S. Government Money Market Portfolio.

The Portfolio follows a disciplined investment process that attempts to provide stability of principal, liquidity and current income through all market conditions, by investing in high quality money market instruments. Among other things, the Portfolio’s investment adviser conducts its own credit analyses of potential investments and portfolio holdings, and relies substantially on a dedicated short-term credit research team. In addition, the Portfolio follows regulatory requirements applicable to money market funds. Those requirements are intended to limit the risks of investing in a money market fund by requiring the Portfolio generally to invest in high quality securities with short-term remaining maturities, and be diversified as to issuers, guarantors and other liquidity providers. All securities held by the Portfolio are U.S. dollar-denominated, and they may have fixed, variable or floating interest rates. The Portfolio’s weighted average maturity may not exceed 90 days, and is typically much shorter.

The Portfolio attempts to meet its investment objective by investing in, among other things:

▪

Repurchase agreements collateralized with high quality securities and other assets.

Principal Investment Risks

In addition, the Fund is subject to the following risks:

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

•

Repurchase Agreement Risk : If a seller is unable to honor its commitments, the Portfolio could lose money.

▪

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

Performance

The bar chart and table below provide some indication of the risks of investing in the U.S. Government Fund (as represented by the performance of the Fund’s Institutional Class) by illustrating the variability of the Fund’s returns during the years since inception. The Fund’s past performance does not necessarily indicate how the Fund will perform in the future. Performance history will be available for the Service Class of the Fund after it has been in operation for one calendar year. The Institutional Class has lower expenses and higher expected returns than the Service Class. The primary difference in expenses is that the Institutional Class does not bear shareholder servicing fees. Please call (877) 521-4083 for the Fund’s current 7-day yield.

State Street Institutional

U.S. Government Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			2.17	%
2009:		___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

		Past 1-Year				Since the Inception Date of the Fund (Annualized)
State Street Institutional U.S. Government Money Market Fund- Institutional Class			______	%			______	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	10,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

By Mail :

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

STATE STREET INSTITUTIONAL TREASURY MONEY MARKET FUND

Investment Objective

The investment objective of the Treasury Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Service Class of the Treasury Fund. As a shareholder in the State Street Treasury Portfolio (the “Treasury Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.10%
Other Expenses	___ %
-Service Fee	0.05%
Total Annual Fund Operating Expenses	___ %

(1)	Amounts reflect the total expenses of the Treasury Portfolio and the Fund.

Example

This Example is intended to help you compare the cost of investing in the Treasury Fund with the cost of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The Treasury Fund invests substantially all of its investable assets in the Treasury Money Market Portfolio.

Principal Investment Risks

▪

Risks of Investing Principally in Money Market Instruments:

▪

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

Performance

The bar chart and table below provide some indication of the risks of investing in the Treasury Fund (as represented by the performance of the Fund’s Institutional Class) by illustrating the variability of the Fund’s returns during the years since inception. The Fund’s past performance does not necessarily indicate how the Fund will perform in the future. Performance history will be available for the Service Class of the Fund after it has been in operation for one calendar year. The Institutional Class has lower expenses and higher expected returns than the Service Class. The primary difference in expenses is that the Institutional Class does not bear shareholder servicing fees. Please call (877) 521-4083 for the Fund’s current 7-day yield.

State Street Institutional Treasury Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			1.24	%
2009:		___		%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

		Past 1-Year				Since the Inception Date of the Fund (Annualized)
State Street Institutional Treasury Money Market Fund- Institutional Class			___	%			_____	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	10,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

By Mail :

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

STATE STREET INSTITUTIONAL TREASURY PLUS MONEY MARKET FUND

Investment Objective

The investment objective of the Treasury Plus Fund as stated above may be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Service Class of the Treasury Plus Fund. As a shareholder in the State Street Treasury Plus Portfolio (the “Treasury Plus Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.10%
Other Expenses	___ %
-Service Fee	0.05%
Total Annual Fund Operating Expenses	___ %

(1)

Amounts reflect the total expenses of the Treasury Plus Portfolio and the Fund.

Example

This Example is intended to help you compare the cost of investing in the Treasury Plus Fund with the cost of investing in other mutual funds.

1 Year

3 Years

5 Years

10 Years

___

Principal Investment Strategies

The Treasury Plus Fund invests substantially all of its investable assets in the Treasury Plus Money Market Portfolio.

Principal Investment Risks

▪

Risks of Investing Principally in Money Market Instruments:

▪

•

Master/Feeder Structure Risk : The Fund’s performance may suffer as a result of large cash inflows or outflows of the Master Portfolio in which the Fund invests.

▪

Repurchase Agreement Risk : If a seller is unable to honor its commitments, the Portfolio could lose money.

Please refer to “Additional Information About Principal Risks of Investing in the Funds and Portfolios” in the Prospectus for further details.

Performance

The bar chart and table below provide some indication of the risks of investing in the Treasury Plus Fund (as represented by the performance of the Fund’s Institutional Class) by illustrating the variability of the Fund’s returns during the years since inception. The Fund’s past performance does not necessarily indicate how the Fund will perform in the future. Performance history will be available for the Service Class of the Fund after it has been in operation for one calendar year. The Institutional Class has lower expenses and higher expected returns than the Service Class. The primary difference in expenses is that the Institutional Class does not bear shareholder servicing fees. Please call (877) 521-4083 for the Fund’s current 7-day yield.

State Street Institutional

Treasury Plus Money Market Fund

Total Return for the Calendar Years Ended December 31

Bar Chart:

2008:			1.55	%
2009:			___	%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended___) and the lowest return for a quarter was ___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

		Past 1-Year				Since the Inception Date of the Fund (Annualized)
State Street Institutional Treasury Plus Money Market Fund- Institutional Class			___	%			______	%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	10,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

By Mail :

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

Additional Information About Principal Risks of Investing in the Funds and Portfolios

Additional information about risks associated with some of the Funds’ and Portfolios’ investment policies and investment strategies is provided below.

•

Banking Industry Risk. If a Portfolio concentrates more than 25% of its assets in bank obligations, adverse developments in the banking industry may have a greater effect on that Portfolio than on a mutual fund that invests more broadly. Banks may be particularly sensitive to certain economic factors such as interest rate changes, adverse developments in the real estate market, fiscal and monetary policy and general economic cycles. Recent instability in the financial markets has heavily influenced the bank obligations of certain financial institutions, resulting in some cases in extreme price volatility and a lack of liquidity. Governments or their agencies may acquire distressed assets from financial institutions and ownership interests in those institutions. The implications of government ownership and disposition of these assets are unclear, and such a program may have positive or negative effects on the liquidity, valuation and performance of certain bank obligations. [ILR Fund]

•

▪

Prepayment Risk and Extension Risk. Prepayment risk and extension risk apply primarily to asset-backed and mortgage-backed securities and certain municipal securities.

•

Liquidity Risk. Adverse market or economic conditions or investor perceptions may result in little or no trading activity in one or more particular securities, thus, making it difficult for a Portfolio holding the securities to determine their values. A Portfolio holding those securities may have to value them at prices that reflect unrealized losses, or if it elects to sell them, it may have to accept lower prices than the prices at which it is then valuing them. The Portfolio also may not be able to sell the securities at any price. [All Funds]

•

Master/Feeder Structure Risk. Unlike traditional mutual funds that invest directly in securities, each of the Funds pursues its objective by investing substantially all of its assets in the Master Portfolio with substantially the same investment objectives, policies and restrictions. The ability of a Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of a Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the corresponding Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio. The Adviser also serves as investment adviser to the Portfolio. Therefore, conflicts may arise as the Adviser fulfills its fiduciary responsibilities to a Fund and its corresponding Portfolio. For example, the Adviser may have an economic incentive to maintain a Fund's investment in the Portfolio at a time when it might otherwise not choose to do so. [All Funds]

•

Money Market Risk. An investment in the Funds is not a deposit of any bank and is not insured or guaranteed by the FDIC or any other government agency. Although the Funds seek to preserve the value of your investment at $1.00 per share, there can be no assurance that they will do so, and it is possible to lose money by investing in the Funds. [All Funds]

•

▪

Municipal Obligations Risk. The values of municipal obligations can fluctuate and may be affected by adverse tax, legislative, or political changes, and by financial developments affecting municipal issuers. Because many municipal obligations are issued to finance specific projects, especially those relating to education, health care, housing, utilities, and water and sewer projects, conditions in these sectors can affect the overall municipal market. Payment of municipal obligations may depend on an issuer’s general unrestricted revenues, revenue generated by a specific project or the operator of a project, government appropriations, or aid from other governments. There is greater credit risk if investors can look only to the revenue generated by a project or the operator of the project because of the relatively limited source of revenue. In addition, future changes in federal tax laws or the activity of an issuer may adversely affect the tax-exempt status of municipal obligations, causing interest received and distributed to shareholders by the Portfolio to be taxable and resulting in a significant decline in the values of such municipal obligations. There is generally less public information available for municipal obligations compared to corporate equities or debt securities, and the investment performance of a Portfolio holding municipal obligations may therefore be more dependent on the analytical abilities of the Portfolio’s adviser.

•

Repurchase Agreement Risk. A repurchase agreement is an agreement to buy a security from a seller at one price and a simultaneous agreement to sell it back to the original seller at an agreed-upon price. Repurchase agreements may be viewed as loans made by the Portfolio which are collateralized by the securities subject to repurchase. The Portfolio’s investment return on such transactions will depend on the counterparties’ willingness and ability to perform their obligations under the repurchase agreements. If the Portfolio’s counterparty should default on its obligations and the Portfolio is delayed or prevented from recovering the collateral, or if the value of the collateral is insufficient, the Portfolio may realize a loss. [ILR Fund, U.S. Government Fund and Treasury Plus Fund]

•

U.S. Government Sponsored Enterprises Risk. U.S. government securities are securities issued or guaranteed as to the payment of interest or principal by the U.S. government, by an agency or instrumentality of the U.S. government, or by a U.S. government-sponsored entity. Certain U.S. government securities may not be supported as to the payment of principal and interest by the full faith and credit of the U.S. government or the ability to borrow from the U.S. Treasury. Some U.S. government securities may be supported as to the payment of principal and interest only by the credit of the entity issuing or guaranteeing the security. Investments in U.S. government sponsored enterprises may return less than investments in non-government fixed-income securities. [ILR Fund and U.S. Government Fund]

Additional Information about the Funds’ and Portfolios’ Investment Strategies and Risks

Section 4(2) Commercial Paper and Rule 144A Securities . A Portfolio may invest in commercial paper issued in reliance on the private placement exemption from registration afforded by Section 4(2) of the Securities Act of 1933, as amended (the ‘‘1933 Act’’). This commercial paper is commonly called ‘‘Section 4(2) paper.’’ A Portfolio may also invest in securities that may be offered and sold only to ‘‘qualified institutional buyers’’ under Rule 144A of the 1933 Act (‘‘Rule 144A securities’’).

Variable and Floating Rate Securities. Variable and floating rate securities are instruments issued or guaranteed by entities such as: (1) the U.S. Government, or an agency or instrumentality thereof, (2) corporations, (3) financial institutions, (4) insurance companies, or (5) trusts. A Portfolio may purchase variable and floating rate securities issued or guaranteed by the U.S. government, or an agency or instrumentality thereof. A variable rate security provides for the automatic establishment of a new interest rate on set dates. Variable rate obligations whose interest is readjusted no less frequently than annually will be deemed to have a maturity equal to the period remaining until the next readjustment of the interest rate. A floating rate security provides for the automatic adjustment of its interest rate whenever a specified interest rate changes. Interest rates on these securities are ordinarily tied to, and are a percentage of, a widely recognized interest rate, such as the yield on 90-day U.S. Treasury bills or the prime rate of a specified bank. Generally, changes in interest rates will have a smaller effect on the market value of variable and floating rate securities than on the market value of comparable fixed-income obligations. Thus, investing in variable and floating rate securities generally allows less opportunity for capital appreciation and depreciation than investing in comparable fixed income securities. Securities purchased by a Portfolio may include variable and floating rate instruments, which may have a stated maturity in excess of the Portfolio’s maturity limitations but which will, except for certain U.S. government obligations, permit the Portfolio to demand payment of the principal of the instrument at least once every 13 months upon not more than 30 days’ notice. Variable and floating rate instruments may include variable amount master demand notes that permit the indebtedness thereunder to vary in addition to providing for periodic adjustments in the interest rate. There may be no active secondary market for a particular variable or floating rate instrument. Nevertheless, the periodic readjustments of their interest rates tend to assure that their value to a Portfolio will approximate their par value. Illiquid variable and floating rate instruments (instruments which are not payable upon seven days’ notice and do not have an active trading market) are subject to a Portfolio’s percentage limitations regarding securities that are illiquid or not readily marketable. The Adviser will continuously monitor the creditworthiness of issuers of variable and floating rate instruments in which the Portfolios invest, and their ability to repay principal and interest. Variable and floating rate securities are subject to interest rate and credit/default risk. [ILR Fund, Tax Free Fund and U.S. Government Fund]

Portfolio Holdings Disclosure

The Funds’ portfolio holdings disclosure policy is described in the SAI.

Management and Organization

The Adviser’s principal address is State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111.

The Administrator and Custodian . State Street Bank and Trust Company (“State Street”), a subsidiary of State Street Corporation, is the administrator and custodian.

The Transfer Agent and Dividend Disbursing Agent . Boston Financial Data Services, Inc. is the transfer agent and dividend disbursing agent.

The Distributor . State Street Global Markets, LLC serves as the Funds’ distributor (the “Distributor”) pursuant to the Distribution Agreement between the Distributor and the Trust.

Shareholder Information

Purchasing Shares . Investors pay no sales load to invest in the Service Class of the Funds. The price for Fund shares is the NAV per share. Orders will be priced at the NAV next calculated after the order is accepted by the Funds.

The minimum initial investment in Service Class shares of the Funds is $10 million, although the Adviser may waive the minimum in its discretion. Holdings of related customer accounts may be aggregated for purposes of determining the minimum investment amount. “Related customer accounts” may include, but are not limited to, accounts held by the same investment or retirement plan, financial institution, broker, dealer or intermediary. The Fund reserves the right to increase or decrease the minimum amount required. There is no minimum subsequent investment, except in relation to maintaining certain minimum account balances (See “Redeeming Shares” below). The Funds intend to be as fully invested as is practicable; therefore, investments must be made in Federal Funds (i.e., monies credited to the account of the Funds’ custodian bank by a Federal Reserve Bank). The Funds require prior notification of subsequent investments in excess of: $5,000,000 for the Tax Free Fund; $10,000,000 for the Treasury Fund; and $50,000,000 for the ILR Fund, U.S. Government Fund, and Treasury Plus Fund.

How to Purchase Shares

By Mail:

An initial investment in the Funds must be preceded or accompanied by a completed, signed Institutional Account Application Form, sent to:

State Street Institutional Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone/Fax:

Ø	confirm receipt of the faxed Institutional Account Application Form (initial purchases only),

Ø	request your new account number (initial purchases only),

Ø	confirm the amount being wired and wiring bank, and

Ø	receive a confirmation number for your purchase order (your trade is not effective until you have received a confirmation number from the Fund).

For your initial investment, send the original, signed Institutional Account Application Form to the address above.

Wire Instructions:

Instruct your bank to transfer money by Federal Funds wire to:

State Street Bank and

Trust Company

2 Avenue de Lafayette

Boston, MA 02111

ABA# 011000028

DDA# 9905-801-8

State Street Institutional Investment Trust ________Fund _______ Class

Account Number

Account Registration

Redeeming Shares. An investor may redeem all or any portion of its investment at the NAV next determined after it submits a redemption request, in proper form, to the Funds. Redemption orders are processed at the NAV next determined after a Fund receives a redemption order in good form. If a Fund receives a redemption order prior to its Valuation Time on a business day, the Fund may send payment for redeemed shares on that day. No dividends will be paid on shares that are redeemed and wired the same day. Otherwise, and except as noted below for the ILR Fund, the shares will normally be redeemed, and payment for redeemed shares sent, on the next business day. Dividends will be earned for the trade date of the redemption but not on the date that the wire is sent. Each Fund, other than the ILR Fund, reserves the right to pay for redeemed shares within seven days after receiving a redemption order if, in the judgment of the Adviser, an earlier payment could adversely affect the Fund. For the ILR Fund, shares are redeemed, and payment for redeemed shares sent, no later than the next business day.

How to Redeem Shares

By Mail

Send a signed letter to:

State Street Institutional Investment Trust Funds

P.O. Box 8048

Boston, MA 02266-8048

The letter should include information necessary to process your request as described below. The Fund may require a medallion guarantee in certain circumstances. See “Medallion Guarantees” below.

By Overnight

State Street Institutional Investment Trust Funds

30 Dan Road

Canton, MA 02021-2809

By Telephone

Please Call (866) 392-0869 between the hours of 8:00 a.m. and 5 p.m. ET.

The Funds will need the following information to process your redemption request:

Ø name(s) of account owners;

Ø account number(s);

Ø the name of the Fund;

Ø your daytime telephone number; and

Ø the dollar amount or number of shares being redeemed.

On any day that the Funds calculate NAV earlier than normal, the Funds reserve the right to adjust the times noted above for purchasing and redeeming shares.

Medallion Guarantees . Certain redemption requests must include a medallion guarantee for each registered account owner if any of the following apply:

Your account address has changed within the last 10 business days.

Redemption proceeds are being transferred to an account with a different registration.

A wire is being sent to a financial institution other than the one that has been established on your Fund account.

Other unusual situations as determined by the Funds’ transfer agent.

The Funds may terminate the receipt of redemption or exchange orders by telephone at any time, in which case you may redeem or exchange shares by other means.

Shareholder Servicing Payments

The Funds’ Service Class shares generally are sold to clients of financial intermediaries (“Service Organizations”), including affiliates of the Adviser, which have entered into shareholder servicing agreements with the Funds or Distributor. Service Organizations agree to perform certain shareholder servicing, administrative and accounting services for their clients and customers who are beneficial owners of shares of the Funds. The Funds will make payments to Service Organizations for services provided at an annual rate of up to 0.05% of a Fund’s average daily net assets attributable to the Service Organization.

Payments to Financial Intermediaries

Dividends, Distributions and Tax Considerations

Financial Highlights

The Financial Highlights table is not presented because Service Class shares of the Funds had not commenced operations as of the date of this Prospectus.

For more information about the Funds :

SSgA FUNDS MANAGEMENT, INC.

STATE STREET FINANCIAL CENTER

ONE LINCOLN STREET

BOSTON, MASSACHUSETTS 02111

The State Street Institutional Investment Trust’s Investment Company Act File Number is 811-09819.

STATE STREET INSTITUTIONAL INVESTMENT TRUST

__________________

STATE STREET INSTITUTIONAL SHORT-TERM TAX EXEMPT BOND FUND (STFLX)

__________________

Prospectus Dated April __, 2010

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

AN INVESTMENT IN THE STATE STREET INSTITUTIONAL SHORT-TERM TAX EXEMPT BOND FUND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY.

TABLE OF CONTENTS

Fund Summary
Additional Information About the Fund’s and Portfolio’s Investment Strategies and Risks
Management and Organization
Shareholder Information
Portfolio Holdings Disclosure
Distribution Servicing Plan and Payments to Financial Intermediaries
Dividends, Distributions and Tax Considerations
Financial Highlights

Fund Summary

This section of the Prospectus is composed of a summary description of the Fund. Additional information about the Fund may be found in the other sections of this Prospectus, the first of which begins on page __ of this Prospectus, as well as the Statement of Additional Information dated April __, 2010 applicable to the Fund.

Investment Objective

The Fund’s investment objective is to seek to provide federally tax-exempt current income and liquidity. The investment objective of the Fund as stated above is fundamental, which means that it may not be changed without shareholder approval.

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. As a shareholder in the Portfolio, the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the estimated expenses of both the Fund and the Portfolio.

Shareholder Fees

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.10%
Distribution (12b-1) Fees	0.05%
Other Expenses	___%
Total Annual Fund Operating Expenses	___%
Less Waivers and Reimbursements (2)	___%
Net Expenses (2)	___ %

(1)	Amounts reflect the total expenses of the Portfolio and the Fund.

(2)	The Adviser has contractually agreed to limit the Fund’s total annual operating expenses (including the pass-through expenses of the Portfolio) to 0.25% (on an annualized basis) of the Fund’s average daily net assets until April 30, 2011.

Example

This Example is intended to help you compare the cost of investing in the Fund with the costs of investing in other mutual funds.

1 Year	3 Years	5 Years	10 Years
$___	$___	$___	$___

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). As a shareholder of the Portfolio the Fund bears its ratable share of the transaction costs associated with the portfolio turnover of the Portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was ___% of the average value of its portfolio.

Principal Investment Strategies

The Fund seeks to achieve its investment objective by investing substantially all of its investable assets in the State Street Institutional Short-Term Tax Exempt Bond Portfolio (the “Portfolio”) of State Street Master Funds, which has the same investment objective as, and investment policies that are substantially similar to those of, the Fund. The Adviser is the investment adviser to the Portfolio. In reviewing the investment objective and strategies of the Fund below, you should assume that the investment objective and strategies of the Portfolio are the same in all material respects as those of the Fund and that, so long as the Fund has invested its assets in the Portfolio, the descriptions below of the Fund’s investment strategies and risks should be read as also applicable to the Portfolio.

The Portfolio has a fundamental policy of investing at least 80% of its net assets under normal market conditions in investment grade municipal securities, the interest from which is, in the opinion of bond counsel, exempt from federal income tax, including the alternative minimum tax. These securities are issued by states, municipalities and their political subdivisions and agencies, instrumentalities and other governmental units, and certain territories and possessions of the United States. Investments may include general obligation bonds and notes, revenue bonds and notes, commercial paper, private placements, tender option bonds, private activity bonds, industrial development bonds and municipal lease contracts. Securities purchased may bear fixed, variable or floating rates of interest or may be zero coupon securities. The Portfolio may buy or sell securities on a when-issued or forward commitment basis. The Portfolio may invest in municipal securities by investing in other mutual funds.

The Portfolio may invest up to 20% of its assets in federally taxable securities including obligations issued by or guaranteed by the U.S. government or its agencies or instrumentalities, certificates of deposit, commercial paper and repurchase agreements.

The municipal debt obligations in which the Portfolio may invest include investments in certain revenue sectors that may be more volatile than others due to changing economic and regulatory issues. These may include industrial development, pollution control, resource recovery, housing, and hospital revenue bond issues. The Portfolio will invest in debt obligations rated, at the time of investment, investment grade by Moody’s, S&P, or comparable quality as determined by the Adviser. The Portfolio does not currently intend to invest in securities subject to the alternative minimum tax.

Investment grade securities are (i) rated in one of the four highest categories (or in the case of commercial paper, in the two highest categories) by at least one nationally recognized statistical rating organization (“NRSRO”); or (ii) if not rated, are of comparable quality, as determined by the Adviser. If a security is downgraded and is no longer investment grade, the Portfolio may continue to hold the security if the Adviser determines that to be in the best interest of the Portfolio.

Principal Risks

Call Risk . The risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as a mortgage-backed security) earlier than expected. This may happen, for example, when there is a decline in interest rates. Under these circumstances, the Portfolio may be unable to recoup all of its initial investment and will also suffer from having to reinvest in lower yielding securities.

Risks of Investing Principally in Fixed Income Instruments:

▪

Interest Rate Risk—The risk that interest rates will rise, causing the value of the fund’s investments to fall.

▪

Credit Risk—The risk that an issuer, guarantor or liquidity provider of an instrument will fail to make scheduled interest or principal payments, which may reduce the fund’s income and the market value of the instrument.

▪

Liquidity Risk—The risk that the fund may not be able to sell some or all of its securities at desired prices, or may be unable to sell the securities at all, because of a lack of demand in the market for such securities, or a liquidity provider defaults on its obligation to purchase the securities when properly tendered by the fund.

Municipal Obligations Risk . Municipal obligations are affected by economic, business and political developments. The yields of municipal securities may move differently and adversely compared to the yields of the overall debt securities markets. Changes in applicable tax laws or tax treatments could reduce or eliminate the current federal income tax exemption on municipal securities or otherwise adversely affect the current federal or state tax status of municipal securities. These securities may be subject to provisions of litigation, bankruptcy and other laws affecting the rights and remedies of creditors, or may become subject to future laws extending the time for payment of principal and/or interest, or limiting the rights of municipalities to levy taxes. The secondary market for municipal bonds also tends to be less well-developed and less liquid than many other debt securities markets. Less liquid obligations can become more difficult to value, may be subject to e rratic price movements , and may limit the Portfolio’s ability to acquire and dispose of municipal securities at desirable yield and price levels.

Master/Feeder Structure Risk . Unlike a traditional mutual fund that invests directly in securities, the Fund pursues its objective by investing substantially all of its assets in the Master Portfolio, which has substantially the same investment objectives, policies and restrictions. The ability of the Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of the Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the corresponding Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio. The Adviser also serves as investment adviser to the Portfolio. Therefore, conflicts may arise as the Adviser fulfills its fiduciary responsibilities to the Fund and the Portfolio. For example, the Adviser may have an economic incentive to maintain the Fund’s investment in the Portfolio at a time when it might otherwise choose not to do so.

THE FUND’S SHARES WILL CHANGE IN VALUE, AND YOU COULD LOSE MONEY BY INVESTING IN THE FUND. THE FUND MAY NOT ACHIEVE ITS OBJECTIVE. AN INVESTMENT IN THE FUND IS NOT A DEPOSIT WITH A BANK AND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY .

Performance

The bar chart and table below provide some indication of the risks of investing in the Short-Term Tax Exempt Bond Fund by illustrating the variability of the Fund’s returns during the year since inception. The Fund’s past performance does not necessarily indicate how the Fund will perform in the future.

State Street Institutional Short-Term Tax Exempt Bond Fund Total Return for the Calendar Year Ended December 31

Bar Chart:

2008:

___%

2009

___%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended ____) and the lowest return for a quarter was ___% (quarter ended ____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

	Past 1-Year		Since the Inception Date of the Fund (Annualized)
State Street Institutional Short-Term Tax Exempt Bond Fund	______%		______%

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Nuveen Asset Management (the “Sub-Adviser” or “Nuveen”) serves as the sub-adviser to the Fund.

Tim Ryan is the leader of a team at the Sub-Adviser that is responsible for the day-to-day management of the Fund. Mr. Ryan has served as portfolio manager of the Fund since 2007.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account	$5,000,000
To add to an existing account	No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

BY MAIL:

State Street Institutional Short-Term Tax Exempt Bond Fund

P.O. Box 8048

Boston, MA 02266-8048

BY OVERNIGHT:

State Street Institutional Short-Term Tax Exempt Bond Fund

30 Dan Road

Canton, MA 02021-2809

BY TELEPHONE:

For wire transfer instructions, please call (866) 392-0869 between 8 a.m. and 5 p.m. Eastern time. Redemption

s by telephone are permitted only if you previously have been authorized for these transactions.

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

Additional Information About the Fund’s and Portfolio’s Investment Strategies and Risks

The investment strategies and risks below reflect the Fund’s and Portfolio’s current practices. This information supplements the principal investment strategies and risks explained above.

Commercial Paper, Rule 144A and Other Short-Term Obligations . Commercial paper (including variable amount master notes and funding agreements) are short-term promissory notes issued by corporations, partnerships, trusts or other entities, to finance short-term credit needs. Short-term obligations held by the Portfolio include non-convertible debt securities (e.g., bonds and debentures) with not more than 397 days (13 months) remaining to maturity at the time of purchase. Short-term obligations issued by trusts may include, but are not limited to, mortgage-related or asset-backed debt instruments, including pass-through certificates such as participations in, or Treasury bonds or notes backed by, pools of mortgages, or credit card, automobile or other types of receivables.

Municipal Obligations . Municipal obligations may be issued to obtain funds to be used for various public purposes, including general purpose financing for state and local governments, refunding outstanding obligations, and financings for specific projects or public facilities. General obligations are backed by the full faith and credit of the issuer. These securities include, for example, tax anticipation notes, bond anticipation notes and general obligation bonds. Revenue obligations are generally backed by the revenues generated from a specific project or facility and include industrial development bonds and private activity bonds. Private activity and industrial development bonds are dependent on the ability of the facility’s user to meet its financial obligations and the value of any real or personal property pledged as security for such payment. Private activity and industrial development bonds, although issued by industrial development authorities, may be backed only by the assets of the non-governmental users, and the user, rather than the municipality, assumes the credit risk. A municipal bond, like a bond issued by a corporation or the U.S. government, obligates the obligor on the bond to pay the bondholder a fixed or variable amount of interest periodically, and to repay the principal value of the bond on a specific maturity date. Municipal notes are short-term instruments which are issued and sold in anticipation of a bond sale, collection of taxes or receipt of other revenues.

Some municipal securities are insured by private insurance companies, while others may be supported by letters of credit furnished by domestic or foreign banks. In determining the credit quality of insured or letter of credit backed securities, the Adviser reviews the financial condition and creditworthiness of such parties including insurance companies, banks and corporations.

Portfolio Duration . The Fund will maintain a dollar-weighted average portfolio duration of two years or less. Duration is a measure of the price sensitivity of a security to changes in interest rates. Unlike maturity, which measures the period of time until final payment is to be made on a security, duration measures the dollar-weighted average maturity of a security’s expected cash flows (i.e., interest and principal payments), discounted to their present values, after giving effect to all maturity shortening features, such as call or redemption rights. With respect to a variable or floating-rate instrument, duration is adjusted to indicate the price sensitivity of the instrument to changes in the interest rate in effect until the next reset date. For substantially all securities, the duration of a security is equal to or less than its stated maturity.

Variable and Floating Rate Securities . Variable and floating rate securities are instruments issued or guaranteed by entities such as: (1) the U.S. Government, or an agency or instrumentality thereof, (2) corporations, (3) financial institutions, (4) insurance companies, or (5) trusts. The Portfolio may purchase variable and floating rate securities issued or guaranteed by the U.S. government, or an agency or instrumentality thereof. A variable rate security provides for the automatic establishment of a new interest rate on set dates. Variable rate obligations whose interest is readjusted no less frequently than annually will be deemed to have a maturity equal to the period remaining until the next readjustment of the interest rate. A floating rate security provides for the automatic adjustment of its interest rate whenever a specified interest rate changes. Interest rates on these securities are ordinarily tied to, and are a percentage of, a widely recognized interest rate, such as the yield on 90-day U.S. Treasury bills or the prime rate of a specified bank. Generally, changes in interest rates will have a smaller effect on the market value of variable and floating rate securities than on the market value of comparable fixed-income obligations. Thus, investing in variable and floating rate securities generally allows less opportunity for capital appreciation and depreciation than investing in comparable fixed income securities. Securities purchased by a Portfolio may include variable and floating rate instruments, which may have a stated maturity in excess of the Portfolio’s maturity limitations but which will, except for certain U.S. government obligations, permit the Portfolio to demand payment of the principal of the instrument at least once every 13 months upon not more than 30 days’ notice. Variable and floating rate instruments may include variable amount master demand notes that permit the indebtedness thereunder to vary in addition to providing for periodic adjustments in the interest rate. There may be no active secondary market for a particular variable or floating rate instrument. Nevertheless, the periodic readjustments of their interest rates tend to assure that their value to the Portfolio will approximate their par value. Illiquid variable and floating rate instruments (instruments which are not payable upon seven days’ notice and do not have an active trading market) are subject to the Portfolio’s percentage limitations regarding securities that are illiquid or not readily marketable. The Adviser will continuously monitor the creditworthiness of issuers of variable and floating rate instruments in which the Portfolio invests, and their ability to repay principal and interest. Variable and floating rate securities are subject to interest rate and credit/default risk .

Temporary Defensive Strategy . From time to time, for temporary defensive purposes, the Portfolio may invest without limit in taxable short-term investments. Dividends paid by the Portfolio that are attributable to income earned by the Portfolio from these instruments will be taxable to investors. This temporary defensive strategy may be inconsistent with the Portfolio’s principal investment strategy, and the Portfolio may not achieve its investment objective.

Portfolio Holdings Disclosure

The Fund’s portfolio holdings disclosure policy is described in the Statement of Additional Information.

Management and Organization

The Fund and the Portfolio . The State Street Institutional Short-Term Tax Exempt Bond Fund (the “Fund”) is a mutual fund whose investment objective is to seek to provide federally tax-exempt current income and liquidity. The Fund invests at least 80% of its assets in a diversified portfolio of investment grade municipal debt securities and maintains a dollar-weighted average portfolio duration of two years or less. The Fund is not a money market fund, and the Fund’s net asset value per share will fluctuate. The Fund is a separate, diversified series of the State Street Institutional Investment Trust (the “Trust”), which is an open-end management investment company organized as a business trust under the laws of the Commonwealth of Massachusetts.

The Fund invests as part of a “master-feeder” structure. The Fund will seek to achieve its investment objective by investing all of its investable assets in a separate mutual fund (a “Portfolio”) that has substantially identical investment objective, investment policies, and risks as the Fund. All discussions about the Fund’s investment objective, policies and risks should be understood to refer also to the investment objectives, policies and risks of the Portfolio.

The Fund can withdraw its investment in a Portfolio if, at any time, the Fund’s Board of Trustees determines that it would be in the best interests of the Fund’s shareholders, or if the investment objectives of the Portfolio changed so that they were inconsistent with the objectives of the Fund. If the Fund withdraws its investment from a Portfolio, the Fund may invest all of its assets in another Portfolio that has the same investment objective as the Fund, the Adviser may directly manage the Fund’s assets, or the Board may take such other action it deems appropriate and in the best interests of shareholders of the Fund, which may include liquidation of the Fund.

The Fund has entered into an investment advisory agreement with the Adviser pursuant to which the Adviser will manage the Fund’s assets directly, at an annual rate of .10% of the Fund’s average daily net assets, in the event that the Fund were to cease investing substantially all of its assets in the Portfolio The Adviser does not receive any fees from the Fund under that agreement so long as the Fund continues to invest substantially all of its assets in the Portfolio or in another investment company.

A summary of the factors considered by the Board of Trustees in connection with the renewal of the investment advisory agreement for the Fund is available in the annual report for the Fund, dated December 31, 2009.

Investment Subadviser . The Sub-Adviser . Nuveen, a wholly owned subsidiary of Nuveen Investments, Inc., is organized under the laws of the State of Delaware and an investment adviser registered with the SEC. On November 13, 2007, Nuveen Investments was acquired by investors led by Madison Dearborn Partners, LLC, which is a private equity investment firm based in Chicago, Illinois (the “MDP Acquisition”). The investor group led by Madison Dearborn Partners, LLC includes affiliates of Merrill Lynch, Pierce, Fenner & Smith Incorporated (“Merrill Lynch”). As of September 30, 2009, Nuveen managed more than $68.5 billion in portfolios of municipal securities for a wide array of mutual funds, closed-end funds, retail managed accounts and institutional managed accounts. The Sub-Adviser’s principal address is 333 West Wacker Drive, Chicago, IL 60606.

The Adviser shall pay the Sub-Adviser an advisory fee with respect to the Portfolio at an annual rate of ___%.

A summary of the factors considered by the Board of Trustees in connection with the approval of the investment sub-advisory agreement for the Fund will be available in the Fund’s semi-annual report dated June 30, 2010.

Portfolio Management. Timothy Ryan, CFA, is the Portfolio Manager for the Portfolio.

Additional information about the portfolio managers’ compensation, other accounts managed by the portfolio managers and the portfolio managers’ ownership of securities in the Fund and the Portfolio is available in the Statement of Additional Information (“SAI”).

The Administrator and Custodian . State Street Bank and Trust Company (“State Street”), a subsidiary of State Street Corporation, is the administrator and custodian.

The Transfer Agent and Dividend Disbursing Agent . Boston Financial Data Services, Inc. is the transfer agent and dividend disbursing agent.

The Distributor . State Street Global Markets, LLC. serves as the Fund’s distributor (the “Distributor”) pursuant to the Distribution Agreement between the Distributor and the Trust.

Shareholder Information

Determination of Net Asset Value . The Fund determines the net asset value (“NAV”) per share each business day as of the close of the regular trading session of the New York Stock Exchange (the “NYSE”). Pricing does not occur on NYSE holidays. A business day is one on which the NYSE is open for regular trading. The Federal Reserve is closed on certain holidays on which the NYSE is open. These holidays are Columbus Day and Veteran’s Day. On these holidays, you will not be able to purchase shares by wiring federal funds because federal funds wiring does not occur on days that the Federal Reserve is closed. The NAV per share for the Fund is computed by adding the value of all securities and other assets of the Fund, deducting accrued liabilities, dividing by the number of shares outstanding and rounding to the nearest cent.

Ordinarily, the Fund values each portfolio security based upon the last reported sales price or other market quotation for the security in the market in which the security principally trades. If market quotations are not readily available for a security or if subsequent events suggest that a market quotation is not reliable, the Fund will use the security’s fair value, as determined in accordance with procedures approved by the Board of Trustees. Debt obligation securities maturing within 60 days of the valuation date are valued at amortized cost.

If you hold shares of the Fund through a broker-dealer or other financial intermediary, your intermediary may offer additional services and account features that are not described in this Prospectus. Please contact your intermediary directly for an explanation of these services.

Purchasing Shares . Investors pay no sales load to invest in the Fund. The price for Fund shares is the NAV per share. Purchase orders in good form and payment received the same day by Fed Wire will receive that day’s NAV and will begin earning dividends declared on the following business day. All purchases that are made by check will begin earning dividends the following business day after the purchase date.

The minimum initial investment in the Fund is $5 million, although the Adviser may waive the minimum in its discretion. Holdings of all customer accounts of each Intermediary shall be aggregated for the purpose of determining these account balances. There is no minimum subsequent investment, except in relation to maintaining certain minimum account balances (See “Redeeming Shares” below). The Fund intends to be as fully invested as is practicable; therefore, investments must be made in Federal Funds (i.e., monies credited to the account of the Fund’s custodian bank by a Federal Reserve Bank) received by the Fund before the order will be accepted. The Fund reserves the right to cease accepting investments at any time or to reject any purchase order.

BY MAIL:

An initial investment in the Fund must be preceded or accompanied by a completed, signed Institutional Account Application Form, sent to:

State Street Institutional Short-Term Tax Exempt Bond Fund

P.O. Box 8048

Boston, MA 02266-8048

BY OVERNIGHT:

State Street Institutional Short-Term Tax Exempt Bond Fund

30 Dan Road

Canton, MA 02021-2809

BY TELEPHONE/FAX:

An initial investment in the Fund must be preceded or accompanied by a completed, signed Institutional Account Application Form, faxed to (816) 218-0400. Call the Fund at (866) 392-0869 between the hours of 8:00 a.m. ET and 5:00 p.m. ET to:

confirm receipt of the faxed Institutional Account Application Form (initial purchases only),

request your new account number (initial purchases only),

confirm the amount being wired and wiring bank,

receive a confirmation number for your purchase order (your trade is not effective until you have received a confirmation number from the Fund),

For your initial investment, send the original, signed Institutional Account Application Form to the address above.

WIRE INSTRUCTIONS:

Instruct your bank to transfer money by Federal Funds wire to:

State Street Bank and Trust Company

2 Avenue de Lafayette

Boston, MA 02111

ABA# 011000028

DDA# 9905-801-8

State Street Institutional Short-Term Tax Exempt Bond Fund

Account Number

Account Registration

You will not be able to redeem shares from the account until the original Application has been received. The Fund and its agents are not responsible for transfer errors by the sending or receiving bank and will not be liable for any loss incurred due to a wire transfer not having been received.

Redeeming Shares . An investor may withdraw all or any portion of its investment at the NAV next determined after it submits a withdrawal request, in proper form, to the Fund. Redemption requests must be received prior to 4:00 p.m. ET on a business day to be effective on the date received. Payments of redemption proceeds ordinarily will be sent the next business day. The Fund reserves the right to pay for redeemed shares within seven days after receiving your redemption order if, in the judgment of the Adviser, an earlier payment could adversely affect the Fund. The right of any investor to receive payment with respect to any withdrawal may be suspended or the payment of the withdrawal proceeds postponed during any period in which the NYSE is closed (other than weekends or holidays) or trading on the NYSE is restricted or, to the extent otherwise permitted by the 1940 Act, if an emergency exists.

If you are redeeming some, but not all, of your shares, your remaining account balance should be above $1,000,000 and subsequent purchases of shares of the Fund may be rejected unless, after such purchase, your account balance will be at or greater than $1,000,000. A request for a partial redemption by an investor whose account balance is below the minimum amount or a request for partial redemption by an investor that would bring the account below the minimum amount may be treated as a request for a complete redemption of the account. These minimums may be different for investments made through certain financial intermediaries as determined by their policies and may be waived in the Adviser’s discretion. The Fund reserves the right to modify or waive minimum account requirements at any time with or without prior notice. The Fund also reserves the right to involuntarily redeem an investor’s account if the investor’s account balance falls below the applicable minimum amount due to transaction activity. Notification will be sent to the shareholder and the shareholder will be given 60 days to increase the balance to the required minimum or the account may be closed.

BY MAIL:

Send a signed letter to:

State Street Institutional Short-Term Tax Exempt Bond Fund

P.O. Box 8048

Boston, MA 02266-8048

The letter should include information necessary to process your request as described below. The Fund may require a medallion guarantee in certain circumstances. See “Medallion Guarantees” below.

BY OVERNIGHT:

State Street Institutional Short-Term Tax Exempt Bond Fund

30 Dan Road

Canton, MA 02021-2809

BY TELEPHONE

(866) 392-0869

Between the hours of 8:00 a.m. and 5:00 p.m. ET.

The Fund will need the following information to process your redemption request:

name(s) of account owners;

your Tax ID or Social Security number;

account number(s);

the name of the Fund;

your daytime telephone number; and

the dollar amount or number of shares being redeemed.

On any day that the Fund calculates its NAV earlier than normal, the Fund reserves the right to adjust the times noted above for purchasing and redeeming shares, except the 9:00 a.m. ET beginning time.

Medallion Guarantees . Certain redemption requests must include a medallion guarantee for each registered account owner if any of the following apply:

Your account address has changed within the last 10 business days.

A wire is being made payable to someone other than the account owner.

Redemption proceeds are being transferred to an account with a different registration.

A wire is being sent to a financial institution other than the one that has been established on your Fund account.

Other unusual situations as determined by the Fund’s transfer agent.

The Fund reserves the right to waive medallion guarantee requirements, require a medallion guarantee under other circumstances or reject or delay a redemption if the medallion guarantee is not in good form. Medallion guarantees may be provided by an eligible financial institution such as a commercial bank, a FINRA member firm such as a stock broker, a savings association or a national securities exchange. A notary public cannot provide a medallion guarantee. The Fund reserves the right to reject a medallion guarantee if it is not provided by a STAMP Medallion guarantor.

About Telephone Transactions . Telephone transactions are extremely convenient but are not free from risk. Neither the Fund nor the Fund’s agents will be responsible for any losses resulting from unauthorized telephone transactions if reasonable security procedures are followed. In addition, you are responsible for: (i) verifying the accuracy of all data and information transmitted by telephone, (ii) verifying the accuracy of your account statements immediately upon receipt, and (iii) promptly notifying the Fund of any errors or inaccuracies including, without limitation, any errors or inaccuracies relating to shareholder data or information transmitted by telephone. During periods of heavy market activity or other times, it may be difficult to reach the Fund by telephone. If you are unable to reach us by telephone, consider sending written instructions.

The Fund may terminate the receipt of redemption or exchange orders by telephone at any time, in which case you may redeem or exchange shares by other means.

Policies to Prevent Market Timing . Frequent purchases and redemptions of Fund shares may present risks for other shareholders of the Fund, which may include, among other things, interference in the efficient management of the Fund’s portfolio, dilution in the value of shares held by long-term shareholders, increased brokerage and administrative costs and forcing the Fund to hold excess levels of cash.

The Trust’s Board of Trustees has adopted policies and procedures designed to detect and prevent inappropriate short-term trading activity that is harmful to the Fund. Because most of the interests in the Fund are held by investors indirectly through one or more financial intermediaries, the Fund does not generally have information about the identity of those investors or about transactions effected by those investors. Rather, the Fund and its service providers periodically review cash inflows and outflows from and to those intermediaries in an attempt to detect inappropriate trading activity by investors holding shares through those intermediaries. The Fund may seek to obtain underlying account trading activity information from financial intermediaries when, in the Adviser’s judgment, the trading activity suggests possible market timing. There is no assurance that the Fund or the Adviser will be able to determine whether trading in the Fund’s shares by an investor holding shares through a financial intermediary is engaged in trading activity that may be harmful to the Fund or its shareholders.

The Fund reserves the right in its discretion to reject any purchase, in whole or in part including, without limitation, by a person whose trading activity in Fund shares the Adviser believes could be harmful to the Fund. The Fund may decide to restrict purchase activity in its shares based on various factors, including, without limitation, whether frequent purchase and sale activity will disrupt portfolio management strategies or adversely affect performance. There can be no assurance that the Fund, the Adviser or State Street will identify all frequent purchase and sale activity affecting the Fund.

Distribution/Servicing (Rule 12b-1) Plan

The Fund has adopted a distribution plan under which the Fund may compensate its distributor (or others) for services in connection with the distribution of the Fund’s shares and for services provided to Fund shareholders. The plan calls for payments at an annual rate (based on average daily net assets) of 0.05%. Because these fees are paid out of the Fund’s assets on an ongoing basis, they will increase the cost of your investment and may cost you more over time than paying other types of sales charges.

Additional Payments to Financial Intermediaries

The Adviser, or an affiliate of the Adviser, out of its own resources, and without additional cost to the Fund and its shareholders, may make additional payments to financial intermediaries (including affiliates of the Adviser) whose client or customer invests in the Fund. Generally, such financial intermediaries may (though they will not necessarily) provide shareholder servicing and support for their customers who purchase shares of the Fund. Not all financial intermediaries receive additional compensation and the amount of compensation paid varies for each financial intermediary. If payments to financial intermediaries by a particular mutual fund complex’s distributor or adviser exceed payments by other mutual fund complexes, your financial adviser and the financial intermediary employing him or her may have an incentive to recommend that fund complex over others. Please speak with your financial adviser to learn more about the total amounts paid to your financial adviser and his or her firm by the Adviser and its affiliates, and by sponsors of other mutual funds he or she may recommend to you. You should also consult disclosures made by your financial intermediary at the time of purchase.

Dividends, Distributions and Tax Considerations

The Fund intends to declare dividends on shares from net investment income daily and have them payable as of the last business day of each month. Distributions from capital gains, if any, will be made annually in December.

The following discussion is a summary of some important U.S. federal tax considerations generally applicable to investments in the Fund. Your investment in the Fund may have other tax implications. Please consult your tax advisor about foreign, federal, state, local or other tax laws applicable to you. Investors, including non-U.S. investors should consult the SAI for more information.

The Fund intends to elect to be treated and qualify each year as a regulated investment company. A regulated investment company is generally not subject to tax at the corporate level on income and gains that are distributed to shareholders. However, the Fund’s failure to qualify as a regulated investment company would result in corporate-level taxation, and consequently, a reduction in income available for distribution to shareholders.

Distributions from the Fund properly designated as “exempt-interest dividends” are not generally subject to federal income tax, including the federal alternative minimum tax for both individual and corporate shareholders but may be subject to state and local taxes. If you receive Social Security or railroad retirement benefits, you should consult your tax adviser to determine what effect, if any, an investment in the Fund may have on the federal taxation of your benefits. Distributions of the Fund’s income other than exempt-interest dividends generally will be taxable as ordinary income, and distributions of the Fund’s net long-term and short-term capital gains (if any) generally will be taxable to you as long-term or short-term capital gain, as applicable, including in respect of gains generated from the sale or other disposition of tax-exempt municipal obligations. The Portfolio may also invest a portion of its assets in securities that generate income (that will be allocated to and distributed by the Fund) that will be subject to both federal and state taxes.

For federal income tax purposes, distributions of investment income (other that “exempt interest dividends” described above) are generally taxable to you as ordinary income. Taxes on distributions of capital gains are determined by how long the Portfolio owned the investments that generated them, rather than how long you have owned your Fund shares. Distributions of net capital gains (that is, the excess of net long-term capital gains over net short-term capital losses) from investments that the Portfolio owned for more than one year and that are properly designated by the Fund as capital gain dividends generally will be taxable as long-term capital gains. Generally, the Fund does not expect a significant portion of its distributions to be capital gain dividends. For individual taxpayers, long-term capital gain rates have been temporarily reduced-in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets-for taxable years beginning before January 1, 2011. Distributions of gains from the sale of investments that the Portfolio owned for one year or less generally will be taxable to you as ordinary income. For taxable years beginning before January 1, 2011, distributions of investment income designated by the Fund as derived from “qualified dividend income” are taxed at the rates applicable to long-term capital gain provided holding period and other requirements are met by both the shareholder and the Fund; however, the Fund does not expect a significant portion of Fund distributions to be derived from qualified dividend income. Distributions (other than distributions of exempt-interest dividends) are taxable whether you receive them in cash or reinvest them in additional shares.

Any gains resulting from the redemption or exchange of your Fund shares will generally be taxable to you as either short-term or long-term capital gain, depending upon how long you have held your shares in the Fund.

Financial Highlights

The Financial Highlights table is intended to help you understand the Fund’s financial performance since inception. Certain information reflects financial results for a single share. The total return in the table represents the rate that an investor would have earned (or lost) on an investment in the Fund’s shares (assuming reinvestment of all dividends and distributions). This information has been audited by___________, whose report, along with the Fund’s financial statements, is included in the Fund’s annual report, which is available upon request. The financial information included in this table should be read in conjunction with the financial statements incorporated by reference in the SAI.

For more information about STATE STREET INSTITUTIONAL SHORT-TERM TAX EXEMPT BOND FUND:

The SAI and the Fund’s annual and semi-annual reports are available, without charge, upon request. Shareholders in the Fund may make inquiries to the Fund to receive such information by calling State Street Global Markets, LLC at (800) 997-7327 or by writing to the Fund, c/o State Street Global Markets, LLC, State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111-2900. These documents are also available on the Fund’s website at http://www.sttfunds.com.

Information about the Fund (including the SAI) can be reviewed and copied at the Commission’s Public Reference Room in Washington, D.C. Information on the operation of the Public Reference Room may be obtained by calling the Commission at 1-202-942-8090. Reports and other information about the Fund are available free of charge on the EDGAR Database on the Commission’s Internet site at http://www.sec.gov. Copies of this information also may be obtained, after paying a duplicating fee, by electronic request at the following E-mail address: publicinfo@sec.gov, or by writing the Commission’s Public Reference Section, Washington, D.C. 20549-1520.

SSgA FUNDS MANAGEMENT, INC.

STATE STREET FINANCIAL CENTER

ONE LINCOLN STREET

BOSTON, MASSACHUSETTS 02111

The State Street Institutional Investment Trust’s Investment Company Act File Number is 811-09819.

STATE STREET INSTITUTIONAL INVESTMENT TRUST

_______________

STATE STREET EQUITY 500 INDEX FUND (STFAX)

ADMINISTRATIVE SHARES

_______________

PROSPECTUS DATED APRIL__, 2010

_______________

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE. THIS FUND OFFERS THREE CLASSES OF SHARES: ADMINISTRATIVE CLASS, SERVICE CLASS AND R CLASS. THIS PROSPECTUS COVERS ONLY THE ADMINISTRATIVE CLASS.

AN INVESTMENT IN THE STATE STREET EQUITY 500 INDEX FUND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY.

Fund Summary
Other Investment Considerations and Risks
Management and Organization
Shareholder Information
Portfolio Holdings Disclosure
Distribution Servicing Plan
Payments to Financial Intermediaries
Dividends, Distributions and Tax Considerations
Financial Highlights

Fund Summary

Investment Objective

The Fund’s investment objective is to replicate as closely as possible, before expenses, the performance of the Standard & Poor’s 500 Index (the “S&P 500” or the “Index”).

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold Administrative Shares of the Fund. As a shareholder in the State Street Equity 500 Index Portfolio (the “Equity 500 Index Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.045%
Distribution (12b-1) Fees	0.15%
Other Expenses	___%
Total Annual Fund Operating Expenses	___%

____________

(1)	Amounts reflect the total expenses of the corresponding Portfolio of the State Street Master Funds and the Fund.

Example

This Example is intended to help you compare the cost of investing in the Fund’s Administrative Shares with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund’s Administrative Shares for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, that all dividends and distributions are reinvested, and that the Fund’s Administrative Shares’ operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

1 YEAR	3 YEARS	5 YEARS	10 YEARS
$___	$___	$___	$___

Portfolio Turnover

Principal Investment Strategies

There is no assurance that the Fund will achieve its investment objective, and you could lose money by investing in the Fund. The Fund seeks to achieve its investment objective by investing substantially all of its investable assets in a corresponding portfolio (the “Portfolio”) of State Street Master Funds that has the same investment objective as, and investment policies that are substantially similar to those of, the Fund.

The Portfolio uses a passive management strategy designed to track the performance of the S&P 500. The Index is a well-known stock market index that includes common stocks of 500 companies from several industrial sectors representing a significant portion of the market value of all stocks publicly traded in the United States.

The Portfolio is not managed according to traditional methods of “active” investment management, which involve the buying and selling of securities based upon economic, financial and market analysis and investment judgment. Instead, the Portfolio, using a “passive” or “indexing” investment approach, attempts to replicate, before expenses, the performance of the S&P 500.

The Portfolio generally intends to invest in all 500 stocks comprising the S&P 500 in proportion to their weightings in the Index. However, under various circumstances, it may not be possible or practicable to purchase all 500 stocks in those weightings. In those circumstances, the Portfolio may purchase a sample of the stocks in the Index in proportions expected by the Adviser to match generally the performance of the Index as a whole. In addition, from time to time stocks are added to or removed from the Index. The Portfolio may sell securities that are represented in the Index, or purchase securities that are not yet represented in the Index, in anticipation of their removal from or addition to the Index. Under normal market conditions, the Portfolio will not invest less than 80% of its total assets in stocks in the Index. Shareholders will receive 60 days’ notice prior to a change in the 80% investment policy.

In addition, the Portfolio may at times purchase or sell futures contracts on the Index, or options on those futures, in lieu of investing directly in the stocks making up the Index. The Portfolio might do so, for example, in order to increase its investment exposure pending investment of cash in the stocks comprising the Index. Alternatively, the Portfolio might use futures or options on futures to reduce its investment exposure in situations where it intends to sell a portion of the stocks in its portfolio but the sale has not yet been completed. The Portfolio may also enter into other derivatives transactions, including the use of options or swap transactions, to assist in attempting to replicate the performance of the Index. The Portfolio may also, to the extent permitted by applicable law, invest in shares of other mutual funds whose investment objectives and policies are similar to those of the Portfolio.

Principal Risks

General risks associated with the Fund’s and Portfolio’s investment policies and investment strategies are discussed below.

·	Stock values could decline generally or could under-perform other investments.

Because the S&P 500 includes mainly large U.S. companies, the Portfolio’s emphasis on securities issued by large capitalization companies makes it susceptible to the risks of investing in larger companies. For example, larger companies may be unable to respond as quickly as smaller companies to competitive challenges. Larger companies also tend not to be able to maintain the high growth rates of well-managed smaller companies, especially during strong economic periods.

The Portfolio’s return may not match the return of the Index for a number of reasons. For example, the return on the securities and other investments selected by the Adviser may not correlate precisely with the return on the Index. The Portfolio incurs a number of operating expenses not applicable to the Index, and incurs costs in buying and selling securities. The Portfolio may not be fully invested at times, either as a result of cash flows into or out of the Portfolio or reserves of cash held by the Portfolio to meet redemptions. The return on the sample of securities purchased by the Portfolio, or futures or other derivative positions taken by the Portfolio, to replicate the performance of the Index may not correlate precisely with the return on the Index.

Derivatives Risk . Derivative transactions typically involve leverage and may be highly volatile. It is possible that a derivative transaction will result in a loss greater than the principal amount invested, and the Portfolio may not be able to close out a derivative transaction at a favorable time or price.

Master/Feeder Structure Risk . Unlike a traditional mutual fund that invests directly in securities, the Fund pursues its objective by investing substantially all of its assets in the Master Portfolio with substantially the same investment objectives, policies and restrictions. The ability of the Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of the Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the corresponding Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio. The Adviser also serves as investment adviser to the Portfolio. Therefore, conflicts may arise as the Adviser fulfills its fiduciary responsibilities to the Fund and its corresponding Portfolio. For example, the Adviser may have an economic incentive to maintain the Fund’s investment in the Portfolio at a time when it might otherwise choose not to do so.

THE FUND’S SHARES WILL CHANGE IN VALUE, AND YOU COULD LOSE MONEY BY INVESTING IN THE FUND. THE FUND MAY NOT ACHIEVE ITS INVESTMENT OBJECTIVE. AN INVESTMENT IN THE FUND IS NOT A DEPOSIT WITH A BANK AND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY.

Performance

The bar chart below shows the performance of the Fund’s Administrative Shares during the Fund’s complete calendar years since inception. The chart provides some indication of the risks of investing in the Fund’s Administrative Shares by showing changes in the Administrative Shares’ performance from year to year. Please keep in mind that past performance does not necessarily indicate how the Fund’s Administrative Shares will perform in the future.

State Street Equity 500 Index Fund

Administrative Shares

Total Return For The Calendar Years

Ended December 31

BAR CHART:

2002:	-22.31%
2003:	28.37%
2004:	10.63%
2005:	4.66%
2006:	15.52%
2007:	5.35%
2008:	-36.89%
2009:	_____%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ____% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

Administrative Shares

The information in the following table gives some indication of the risks of an investment in the Fund’s Administrative Shares by comparing the Administrative Shares’ performance to the performance of the S&P 500 over various periods of time.

The Fund’s Administrative Shares’ after-tax returns listed below are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Additionally, actual after-tax returns depend on an investor’s tax situation and may differ from those shown below, and after-tax returns are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

	PAST 1-YEAR	PAST 5-YEAR	SINCE THE INCEPTION DATE OF THE FUND (ANNUALIZED)
State Street Equity 500 Index Fund Return Before Taxes	___%	___%	___%
Return After Taxes on Distributions	___%	___%	___%
Return After Taxes on Distributions and Sale of Fund Shares	___%	___%	___%
S&P 500 (reflects no deduction for expenses of taxes)	___%	___%	___%

____________

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

John A. Tucker has been a Portfolio Manager for the Portfolio since 2007. Karl Schneider has been a Portfolio Manager for the Portfolio since 2002.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account	$25,000,000
To add to an existing account	No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

BY MAIL:

State Street Equity 500 Index Fund

P.O. Box 5493

Boston, MA 02206

BY OVERNIGHT:

State Street Equity 500 Index Fund

200 Clarendon Street

Boston, MA 02116

BY TELEPHONE:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

Other Investment Considerations and Risks

Changes in Policies . The Trust’s Board of Trustees may change the Fund’s investment strategies and other policies without shareholder approval, except as otherwise indicated. The Board of Trustees will not materially change the Fund’s investment objective without shareholder approval.

The S&P 500 . The S&P 500 is a well-known stock market index that includes common stocks of 500 companies from several industrial sectors representing a significant portion of the market value of all common stocks publicly traded in the United States, most of which are listed on the New York Stock Exchange, Inc. (the “NYSE”). Stocks in the S&P 500 are weighted according to their float adjusted market capitalizations (i.e., the number of shares outstanding multiplied by the stock’s current price). The companies selected for inclusion in the S&P 500 are those of large publicly held companies which generally have the largest market values within their respective industries. The composition of the S&P 500 is determined by Standard & Poor’s and is based on such factors as the market capitalization and trading activity of each stock and its adequacy as a representation of stocks in a particular industry group, and may be changed from time to time. “Standard & Poor’s(R),” “S&P,” “S&P 500,” “Standard & Poor’s 500” and “500” are trademarks of The McGraw-Hill Companies, Inc. and have been licensed for use by the Fund. The Fund is not sponsored, endorsed, sold or promoted by S&P, and S&P makes no representation regarding the advisability of investing in the Fund.

Index Futures Contracts and Related Options . The Portfolio may buy and sell futures contracts on the Index and options on those futures contracts. An “index futures” contract is a contract to buy or sell units of an index at an agreed price on a specified future date. Depending on the change in value of the Index between the time when the Portfolio enters into and closes out an index future or option transaction, the Portfolio realizes a gain or loss. Options and futures transactions involve risks. For example, it is possible that changes in the prices of futures contracts on the Index will not correlate precisely with changes in the value of the Index. In those cases, use of futures contracts and related options might decrease the correlation between the return of the Portfolio and the return of the Index. In addition, the Portfolio incurs transaction costs in entering into, and closing out, positions in futures contracts and related options. These costs typically have the effect of reducing the correlation between the return of the Portfolio and the return of the Index. Because the secondary market for futures contracts and options may be illiquid, the Portfolio may have to hold a contract or option when the Adviser would otherwise have sold it, or it may only be able to sell at a price lower than what the Adviser believes is the fair value of the contract or option, thereby potentially reducing the return of the Portfolio.

Other Derivative Transactions . The Portfolio may enter into derivatives transactions involving options and swaps. These transactions involve many of the same risks as those described above under “Index Futures Contracts and Related Options.” In addition, since many of such transactions are conducted directly with counterparties, and not on an exchange or board of trade, the Portfolio’s ability to realize any investment return on such transactions may depend on the counterparty’s ability or willingness to meet its obligations.

Securities Lending . The Portfolio may lend portfolio securities with a value of up to 33-1/3% of its total assets. For these purposes, total assets shall include the value of all assets received as collateral for the loan. Such loans may be terminated at any time, and the Portfolio will receive cash or other obligations as collateral. In a loan transaction, as compensation for lending its securities, the Portfolio will receive a portion of the dividends or interest accrued on the securities held as collateral or, in the case of cash collateral, a portion of the income from the investment of such cash. In addition, the Portfolio will receive the amount of all dividends, interest and other distributions on the loaned securities. However, the borrower has the right to vote the loaned securities. The Portfolio will call loans to vote proxies if a material issue affecting the investment is to be voted upon. Should the borrower of the securities fail financially, the Portfolio may experience delays in recovering the securities or exercising its rights in the collateral. Loans are made only to borrowers that are deemed by the securities lending agent to be of good financial standing. In a loan transaction, the Portfolio will also bear the risk of any decline in value of securities acquired with cash collateral. The Portfolio will attempt to minimize this risk by limiting the investment of cash collateral to high quality instruments of short maturity. This strategy is not used to leverage the Portfolio.

Comparison Index. The S&P 500 is a capitalization-weighted index of 500 industry-leading stocks and is widely regarded to be representative of the stock market in general. The S&P 500 is unmanaged and does not reflect the actual cost of investing in the instruments that comprise the index. Additionally, the returns of the S&P 500 Index do not reflect the effect of fees, expenses and taxes.

Portfolio Holdings Disclosure

The Fund’s portfolio holdings disclosure policy is described in the Statement of Additional Information.

Management and Organization

The Fund and the Portfolio . The State Street Equity 500 Index Fund (the “Fund”) is a separate, diversified series of the State Street Institutional Investment Trust (the “Trust”), which is an open-end management investment company organized as a business trust under the laws of the Commonwealth of Massachusetts.

The Fund invests as part of a “master-feeder” structure. The Fund will seek to achieve its investment objective by investing substantially all of its investable assets in a separate mutual fund (a “Portfolio”) that has a substantially identical investment objective, investment policies, and risks as the Fund. All discussions about the Fund’s investment objective, policies and risks should be understood to refer also to the investment objectives, policies and risks of the Portfolio.

The Equity 500 Index Fund offers three classes of shares: Administrative Shares, Service Shares and Class R Shares. Only the Administrative Shares of the Fund are discussed in this prospectus.

The Adviser . State Street Global Advisors (“SSgA”) is the investment management group of State Street Corporation , a publicly held bank holding company, and includes the Adviser, SSgA FM, a wholly owned subsidiary. SSgA is one of the world’s largest institutional money managers, and uses quantitative and traditional techniques to manage approximately $1.91 trillion as of December 31, 2009 in investment programs and portfolios for institutional and individual investors. SSgA FM, as the investment adviser to the Fund and the Portfolio, is registered with the Securities and Exchange Commission (“SEC”) under the Investment Advisers Act of 1940, as amended. SSgA FM had approximately $168.4 billion in assets under management at December 31, 2009. The Fund has entered into an investment advisory agreement with the Adviser pursuant to which the Adviser will manage the Fund’s assets directly, for compensation paid at an annual rate of 0.10% of the Fund’s average daily net assets, in the event that the Fund were to cease investing substantially all of its assets in the Portfolio. The Adviser does not receive any fees from the Fund under that agreement so long as the Fund continues to invest substantially all of its assets in the Portfolio or in another investment company. The Adviser places all orders for purchases and sales of the Portfolio’s investments.

A summary of the factors considered by the Board of Trustees in connection with the renewal of the investment advisory agreement for the Fund is available in the Fund’s annual report dated December 31, 2009.

The Adviser manages the Portfolio using a team of investment professionals. The team approach is used to create an environment that encourages the flow of investment ideas. The portfolio managers within the team work together in a cohesive manner to develop and enhance techniques that drive the investment process for the respective investment strategy. This approach requires portfolio managers to share a variety of responsibilities including investment strategy and analysis while retaining responsibility for the implementation of the strategy within any particular portfolio. The approach also enables the team to draw upon the resources of other groups within the firm. Each portfolio management team is overseen by the SSgA Investment Committee. Key professionals involved in the day-to-day portfolio management for the Portfolio include the following:

John A. Tucker, CFA

Mr. Tucker is a Managing Director of State Street Global Advisors, a Principal of SSgA FM, and Head of US Equity Markets in the Global Structured Products Group. He is responsible for overseeing the management of all U.S. equity index strategies and Exchange Traded Funds and is a member of the Senior Management Group.

Previously, Mr. Tucker was head of the Structured Products group in SSgA’s London office, where he was responsible for the management of all index strategies in SSgA’s second largest investment center. Prior to joining the investment management group, he was the Operations Manager for SSgA’s International Structured Products group, where he was responsible for the operations staff and functions. He joined State Street in 1988 and has served as a Portfolio Manager of the Portfolio since 2007.

Mr. Tucker received a BA in Economics from Trinity College and an MS in Finance from Boston College. He has also earned the Chartered Financial Analyst designation and is a member of the Boston Security Analysts Society and the CFA Institute.

Karl Schneider

Mr. Schneider is a Vice President of SSgA, a Principal of SSgA FM and a Senior Portfolio Manager within the Global Structured Products Group. Mr. Schneider joined SSgA in 1996 and has served as a Portfolio Manager of the Portfolio since 2002. Mr. Schneider currently manages several of the firm’s commingled US index strategies as well as other separately managed domestic and international funds. Within the Global Structured Products Group, he serves as the point person for synthetic beta and manages several synthetic beta strategies, including commodities, buy/write, and hedge fund replication. Mr. Schneider is also a member of the SSgA Derivatives Committee. Prior to joining the Global Structured Products Group, Mr. Schneider worked as a portfolio manager in SSgA’s Currency Management Group, managing both active currency selection and traditional passive hedging overlay portfolios.

Mr. Schneider holds a Bachelor of Science degree in Finance and Investments from Babson College and also a Master of Science degree in Finance from the Carroll School of Management at Boston College. Additionally, he holds a Series 3 license from the National Futures Association.

Additional information about the portfolio managers’ compensation, other accounts managed by the portfolio managers, and the portfolio managers’ ownership of securities in the Fund and the Portfolio is available in the Statement of Additional Information (“SAI”).

The Adviser’s principal address is State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111.

The Administrator, Custodian, and Transfer Agent and Dividend Disbursing Agent . State Street Bank and Trust Company (“State Street”), a subsidiary of State Street Corporation, is the administrator, custodian, transfer agent and dividend disbursing agent for the Fund.

The Distributor . State Street Global Markets, LLC serves as the Fund’s distributor (the “Distributor”) pursuant to the Distribution Agreement between the Distributor and the Trust.

Shareholder Information

Determination of Net Asset Value . The Fund determines its net asset value (“NAV”) per share once each business day as of the close of regular trading on the NYSE. The NAV per share is based on the market value of the investments held in the Fund. The NAV of the Fund’s Administrative Shares is calculated by dividing the value of the assets of the Fund attributable to its Administrative Shares less the liabilities of the Fund attributable to its Administrative Shares by the number of Administrative Shares outstanding. The Fund values each security or other investment pursuant to guidelines adopted by the Board of Trustees. Securities or other investments may be valued at fair value, as determined in good faith and pursuant to procedures approved by the Portfolio’s Board of Trustees, under certain limited circumstances. For example, fair value pricing may be used when market quotations are not readily available or reliable, such as when (i) trading for a security is restricted; or (ii) a significant event, as determined by the Adviser, that may affect the value of one or more securities or other investments held by the Fund occurs after the close of a related exchange but before the determination of the Fund’s NAV. Attempts to determine the fair value of securities or other investments introduce an element of subjectivity to the pricing of securities or other investments. As a result, the price of a security or other investment determined through fair valuation techniques may differ from the price quoted or published by other sources and may not accurately reflect the price the Fund would have received had it sold the investment. To the extent that the Fund invests in the shares of other registered open-end investment companies that are not traded on an exchange (mutual funds), such shares are valued at their published net asset values per share as reported by the funds. The prospectuses of these funds explain the circumstances under which the funds will use fair value pricing and the effects of using fair value pricing.

Purchasing Shares . Investors pay no sales load to invest in the Fund. The price for Fund shares is the NAV per share. Orders will be priced at the NAV next calculated after the order is accepted by the Fund. The minimum initial investment in the Class is $25 million, although the Adviser may waive the minimum in its discretion. There is no minimum subsequent investment. The Fund intends to be as fully invested as is practicable; therefore, investments must be made either in Federal Funds (i.e., monies credited to the account of the Fund’s custodian bank by a Federal Reserve Bank) or securities (“in-kind”) acceptable to the Adviser. (Please consult your tax adviser regarding in-kind transactions.) The Fund reserves the right to cease accepting investments at any time or to reject any purchase order.

In accordance with certain federal regulations, the Trust is required to obtain, verify and record information that identifies each entity that applies to open an account. For this reason, when you open (or change ownership of) an account, the Trust will request certain information, including your name, address and taxpayer identification number, which will be used to verify your identity. If you are unable to provide sufficient information to verify your identity, the Trust will not open an account for you. As required by law, the Trust may employ various procedures, such as comparing your information to fraud databases or requesting additional information and documentation from you, to ensure that the information supplied by you is correct. The Trust reserves the right to reject any purchase order for any reason, including failure to provide the Trust with information necessary to confirm your identity as required by law.

Redeeming Shares . An investor may withdraw all or any portion of its investment at the NAV next determined after it submits a withdrawal request, in proper form, to the Fund. The Fund will pay the proceeds of the withdrawal either in Federal Funds or in securities at the discretion of the Adviser, normally on the next Fund business day after the withdrawal, but in any event no more than seven days after the withdrawal. (Please consult your tax adviser regarding in-kind transactions.) The right of any investor to receive payment with respect to any withdrawal may be suspended or the payment of the withdrawal proceeds postponed during any period in which the NYSE is closed (other than weekends or holidays) or trading on the NYSE is restricted or, to the extent otherwise permitted by the 1940 Act, as amended, if an emergency exists.

Policies to Prevent Market Timing . Frequent purchases and redemptions of Fund shares may present risks for other shareholders of the Fund, which may include, among other things, interference in the efficient management of the Fund’s portfolio, dilution in the value of Fund shares held by long-term shareholders, increased brokerage and administrative costs and forcing the Fund to hold excess levels of cash.

The Fund is intended as a long-term investment. Therefore, the Trust’s Board of Trustees has adopted policies and procedures designed to detect and prevent inappropriate short-term trading activity that is harmful to the Fund. Because most of the interests in the Fund are held by investors indirectly through one or more financial intermediaries, the Fund does not generally have information about the identity of those investors or about transactions effected by those investors. Rather, the Fund and its service providers periodically review cash inflows and outflows from and to those intermediaries in an attempt to detect inappropriate trading activity by investors holding shares through those intermediaries. The Fund may seek to obtain underlying account trading activity information from financial intermediaries when, in the Adviser’s judgment, the trading activity suggests possible market timing. There is no assurance that the Fund or the Adviser will be able to determine whether trading by an investor holding shares through a financial intermediary is engaged in trading activity that may be harmful to the Fund or its shareholders.

The Fund reserves the right in its discretion to reject any purchase, in whole or in part including, without limitation, by a person whose trading activity in Fund shares the Adviser believes could be harmful to the Fund. The Fund may decide to restrict purchase activity in its shares based on various factors, including, without limitation, whether frequent purchase and sale activity will disrupt portfolio management strategies and adversely affect performance. There can be no assurance that the Fund, the Adviser or State Street will identify all frequent purchase and sale activity affecting the Fund.

Distribution/Servicing (Rule 12b-1) Plan

The Fund has adopted a distribution plan under which the Fund may compensate its distributor (or others) for services in connection with the distribution of the Fund’s Administrative Shares and for services provided to Fund shareholders. The plan calls for payments at an annual rate (based on average daily net assets) of 0.15% of the Fund’s net assets attributable to its Administrative Shares. Because these fees are paid out of the assets of the Fund attributable to its Administrative Shares on an ongoing basis, they will increase the cost of your investment and may cost you more over time than paying other types of sales charges.

Additional Payments to Financial Intermediaries

Dividends, Distributions and Tax Considerations

Income dividends and capital gains distributions of the Fund will be declared and paid at least annually.

The Fund intends to elect to be treated and qualify each year as a regulated investment company. A regulated investment company is generally not subject to tax at the corporate level on income and gains that are distributed to shareholders. However, the Fund’s failure to qualify as a regulated investment company would result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

For federal income tax purposes, distributions of investment income are generally taxable to you as ordinary income. Taxes on distributions of capital gains generally are determined by how long the Portfolio owned the investments that generated them, rather than how long you have owned your Fund shares. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before your investment (and thus were included in the price you paid for your shares). Distributions may also be subject to state and local taxes and are taxable whether you receive them in cash or reinvest them in additional shares. Distributions of net capital gains (that is, the excess of net long-term capital gains over net short-term capital losses) from the sale of investments that the Portfolio owned for more than one year that are properly designated by the Fund as capital gains dividends generally will be taxable to you as long-term capital gains. For individual taxpayers long-term capital gain rates have been temporarily reduced -- in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets -- for taxable years beginning before January 1, 2011. Distributions of gains from investments that the Portfolio owned for one year or less generally will be taxable to you as ordinary income. For the taxable years beginning before January 1, 2011, distributions of investment income designated by the Fund as derived from “qualified dividend income” are taxed at the rates applicable to long-term capital gain, provided holding period and other requirements are met by both the shareholder and the Fund.

Any gain resulting from the sale, exchange, or redemption of your shares will generally also be taxable to you as either short-term or long-term capital gain, depending upon how long you held your shares in the Fund.

Financial Highlights

The Financial Highlights table is intended to help you understand the Fund’s Administrative Shares financial performance for the past 5 years. Certain information reflects financial results for a single share of the Administrative Shares. The total return in the table represents the rate that an investor would have earned (or lost) on an investment in the Fund’s Administrative Shares (assuming reinvestment of all dividends and distributions). This information has been audited by_________, whose report, along with the Fund’s financial statements, is included in the Fund’s annual report, which is available upon request. The financial information included in this table should be read in conjunction with the financial statements incorporated by reference in the Statement of Additional Information.

For more information about STATE STREET EQUITY 500 INDEX FUND:

The Fund’s statement of additional information (SAI) includes additional information about the Fund and is incorporated by reference into this document. Additional information about the Fund’s investments is available in the Fund’s annual and semi-annual reports to shareholders. In the Fund’s annual report, you will find a discussion of the market conditions and investment strategies that significantly affected the Fund’s performance during its last fiscal year.

The SAI and the Fund’s annual and semi-annual reports are available, without charge, upon request. Shareholders in the Fund may make inquiries to the Fund to receive such information by calling (877) 521-4083 or the customer service center at the telephone number shown in the accompanying contract prospectus, if applicable. The Fund does not have an Internet website.

SSgA FUNDS MANAGEMENT, INC.

State Street Financial Center

One Lincoln Street

Boston, Massachusetts 02111

The State Street Institutional Investment Trust’s Investment Company Act File Number is 811-09819.

STATE STREET INSTITUTIONAL INVESTMENT TRUST

_______________

STATE STREET EQUITY 500 INDEX FUND

CLASS R SHARES

_______________

PROSPECTUS DATED APRIL __, 2010

_______________

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE. THIS FUND OFFERS THREE CLASSES OF SHARES: R CLASS, ADMINISTRATIVE CLASS AND SERVICE CLASS. THIS PROSPECTUS COVERS ONLY THE R CLASS.

AN INVESTMENT IN THE STATE STREET EQUITY 500 INDEX FUND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY.

Fund Summary
Other Investment Considerations and Risks
Management and Organization
Shareholder Information
Portfolio Holdings Disclosure
Distribution Servicing Plan and Payments to Financial Intermediaries
Dividends, Distributions and Tax Considerations
Financial Highlights

Fund Summary

Investment Objective

The Fund’s investment objective is to replicate as closely as possible, before expenses, the performance of the Standard & Poor’s 500 Index (the “S&P 500” or the “Index”).

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold Class R Shares of the Fund. As a shareholder in the State Street Equity 500 Index Portfolio (the “Equity 500 Index Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.045%
Distribution (12b-1) Fees	0.60%
Other Expenses	___ %
Total Annual Fund Operating Expenses	___ %

____________

(1)	Amounts reflect the total expenses of the corresponding Portfolio of the State Street Master Funds and the Fund.

Example

This Example is intended to help you compare the cost of investing in the Fund’s Class R Shares with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund’s Class R Shares for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, that all dividends and distributions are reinvested, and that the Fund’s Class R Shares’ operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

1 YEAR	3 YEARS	5 YEARS	10 YEARS
$___	$___	$___	$___

Portfolio Turnover

Principal Investment Strategies

Principal Risks

General risks associated with the Fund’s and Portfolio’s investment policies and investment strategies are discussed below.

·	Stock values could decline generally or could under-perform other investments.

Master/Feeder Structure Risk . Unlike a traditional mutual fund that invests directly in securities, the Fund pursues its objective by investing substantially all of its assets in the Master Portfolio with substantially the same investment objectives, policies and restrictions. The ability of the Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of the Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the corresponding Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio. The Adviser also serves as investment adviser to the Portfolio. Therefore, conflicts may arise as the Adviser fulfills its fiduciary responsibilities to the Fund and its corresponding Portfolio. For example, the Adviser may have an economic incentive to maintain the Fund’s investment in the Portfolio at a time when it might otherwise choose not to do so.

Performance

The bar chart below shows the performance of the Fund’s Class R Shares during the Fund’s complete calendar years since inception. The chart provides some indication of the risks of investing in the Fund’s Class R Shares by showing changes in the Class R Shares’ performance from year to year. Please keep in mind that past performance does not necessarily indicate how the Fund’s Class R Shares will perform in the future. Additionally, the performance information prior to June 7, 2005, the inception date for Class R shares, is that of the Administrative Shares of the Fund, which incur lower expenses and typically experience higher returns than the Class R Shares. The primary difference in expenses is the lower distribution (12b-1) fee of 0.15% for Administrative Shares compared to 0.60% for Class R Shares on an annual basis. The Administrative Shares’ inception date was April 18, 2001.

State Street Equity 500 Index Fund

Class R Shares

Total Return For The Calendar Years

Ended December 31

Bar Chart:

2002:	-22.31%
2003:	28.37%
2004:	10.63%
2005:	4.92%
2006:	15.02%
2007:	4.88%
2008:	-37.20%
2009:	____%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended____) and the lowest return for a quarter was ___% (quarter ended____).

Average Annual Total Returns

For the Periods Ended December 31, 2009

Class R Shares

The information in the following table gives some indication of the risks of an investment in the Fund’s Class R Shares by comparing the Class R Shares’ performance to the performance of the S&P 500 over various periods of time.

The Fund’s Class R Shares’ after-tax returns listed below are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Additionally, actual after tax returns depend on an investor’s tax situation and may differ from those shown below, and after-tax returns are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. Additionally, the performance information prior to June 7, 2005, the inception date for Class R Shares, is that of the Administrative Shares of the Fund, which incur lower expenses and typically experience higher returns than the Class R Shares. The primary difference in expenses is the lower distribution (12b-1) fee of 0.15% for Administrative Shares compared to 0.60% for Class R Shares on an annual basis. The Administrative Shares’ inception date was April 18, 2001.

	PAST 1-YEAR	PAST 5-YEAR	SINCE THE INCEPTION DATE OF THE FUND (ANNUALIZED)
State Street Equity 500 Index Fund
Return Before Taxes	___%	___%	___%
Return After Taxes on Distributions	___%	___%	___%
Return After Taxes on Distributions and Sale of Fund Shares	___%	___%	___%
S&P 500 (reflects no deduction for expenses of taxes)	___%	___%	___%

____________

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

John A. Tucker has been a Portfolio Manager for the Portfolio since 2007. Karl Schneider has been a Portfolio Manager for the Portfolio since 2002.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account	$25,000,000
To add to an existing account	No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

BY MAIL:

State Street Equity 500 Index Fund

P.O. Box 5493

Boston, MA 02206

BY OVERNIGHT:

State Street Equity 500 Index Fund

200 Clarendon Street

Boston, MA 02116

BY TELEPHONE:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

Other Investment Considerations and Risks

Comparison Index. The S&P 500 is a capitalization-weighted index of 500 industry-leading stocks and is widely regarded to be representative of the stock market in general. The S&P 500 is unmanaged and does not reflect the actual cost of investing in the instruments that comprise the index. Additionally, the returns of the S&P 500 do not reflect the effect of fees, expenses and taxes.

Portfolio Holdings Disclosure

The Fund’s portfolio holdings disclosure policy is described in the Statement of Additional Information.

Management and Organization

The Equity 500 Index Fund offers three classes of shares: Administrative Shares, Service Shares and Class R Shares. Only the Class R Shares of the Fund are discussed in this prospectus.

The Adviser . State Street Global Advisors (“SSgA”) is the investment management group of State Street Corporation, a publicly held bank holding company and includes the Adviser, SSgA FM, a wholly-owned subsidiary. SSgA is one of the world’s largest institutional money managers, and uses quantitative and traditional techniques to manage approximately $1.91 trillion as of December 31, 2009 in investment programs and portfolios for institutional and individual investors. SSgA FM, as the investment adviser to the Fund and the Portfolio, is registered with the Securities and Exchange Commission (“SEC”) under the Investment Advisers Act of 1940, as amended. SSgA FM had approximately $168.4 billion in assets under management at December 31, 2009. The Fund has entered into an investment advisory agreement with the Adviser pursuant to which the Adviser will manage the Fund’s assets directly, for compensation paid at an annual rate of 0.10% of the Fund’s average daily net assets, in the event that the Fund were to cease investing substantially all of its assets in the Portfolio. The Adviser does not receive any fees from the Fund under that agreement so long as the Fund continues to invest substantially all of its assets in the Portfolio or in another investment company. The Adviser places all orders for purchases and sales of the Portfolio’s investments.

John A. Tucker, CFA

Karl Schneider

The Adviser’s principal address is State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111.

The Distributor . State Street Global Markets, LLC serves as the Fund’s distributor (the “Distributor”) pursuant to the Distribution Agreement between the Distributor and the Trust.

Shareholder Information

Determination of Net Asset Value . The Fund determines its net asset value (“NAV”) per share once each business day as of the close of regular trading on the NYSE. The NAV per share is based on the market value of the investments held in the Fund. The NAV of the Fund’s R Shares is calculated by dividing the value of the assets of the Fund attributable to its R shares less the liabilities of the Fund attributable to its R shares by the number of R Shares outstanding. The Fund values each security or other investment pursuant to guidelines adopted by the Board of Trustees. Securities or other investments may be valued at fair value, as determined in good faith and pursuant to procedures approved by the Portfolio’s Board of Trustees, under certain limited circumstances. For example, fair value pricing may be used when market quotations are not readily available or reliable, such as when (i) trading for a security is restricted; or (ii) a significant event, as determined by the Adviser, that may affect the value of one or more securities or other investments held by the Fund occurs after the close of a related exchange but before the determination of the Fund’s NAV. Attempts to determine the fair value of securities or other investments introduce an element of subjectivity to the pricing of securities or other investments. As a result, the price of a security or other investment determined through fair valuation techniques may differ from the price quoted or published by other sources and may not accurately reflect the price the Fund would have received had it sold the investment. To the extent that the Fund invests in the shares of other registered open-end investment companies that are not traded on an exchange (mutual funds), such shares are valued at their published net asset values per share as reported by the funds. The prospectuses of these funds explain the circumstances under which the funds will use fair value pricing and the effects of using fair value pricing.

The minimum initial investment in the Class is $25 million, although the Adviser may waive the minimum in its discretion. There is no minimum subsequent investment. The Fund intends to be as fully invested as is practicable; therefore, investments must be made either in Federal Funds (i.e., monies credited to the account of the Fund’s custodian bank by a Federal Reserve Bank) or securities (“in-kind”) acceptable to the Adviser. (Please consult your tax adviser regarding in-kind transactions.) The Fund reserves the right to cease accepting investments at any time or to reject any purchase order.

In accordance with certain federal regulations, the Trust is required to obtain, verify and record information that identifies each entity that applies to open an account. For this reason, when you open (or change ownership of) an account, the Trust will request certain information, including your name, address and taxpayer identification number, which will be used to verify your identity. If you are unable to provide sufficient information to verify your identity, the Trust will not open an account for you. As required by law, the Trust may employ various procedures, such as comparing your information to fraud databases or requesting additional information and documentation from you, to ensure that the information supplied by you is correct. The Trust reserves the right to reject any purchase order for any reason, including failure to provide the Trust with information necessary to confirm your identity as required by law.

Policies to Prevent Market Timing . Frequent purchases and redemptions of Fund shares may present risks for other shareholders of the Fund, which may include, among other things, interference in the efficient management of the Fund’s portfolio, dilution in the value of Fund shares held by long-term shareholders, increased brokerage and administrative costs and forcing the Fund to hold excess levels of cash.

The Fund reserves the right in its discretion to reject any purchase, in whole or in part including, without limitation, by a person whose trading activity in Fund shares the Adviser believes could be harmful to the Fund. The Fund may decide to restrict purchase activity in its shares based on various factors, including, without limitation, whether frequent purchase and sale activity will disrupt portfolio management strategies and adversely affect performance. There can be no assurance that the Fund, the Adviser or State Street will identify all frequent purchase and sale activity affecting the Fund.

Distribution/Servicing (Rule 12b-1 ) Plan

The Fund has adopted a distribution plan under which the Fund may compensate its distributor (or others) for services in connection with the distribution of the Fund’s Class R Shares and for services provided to Fund shareholders. The plan calls for payments at an annual rate (based on average daily net assets) of 0.60% of the Fund’s net assets attributable to its R Shares. Because these fees are paid out of the assets of the Fund attributable to its R Shares, on an ongoing basis, they will increase the cost of your investment and may cost you more over time than paying other types of sales charges.

Additional Payments to Financial Intermediaries

Dividends, Distributions and Tax Considerations

Income dividends and capital gains distributions of the Fund will be declared and paid at least annually.

The Fund intends to elect to be treated and qualify each year as a regulated investment company. A regulated investment company is generally not subject to tax at the corporate level on income and gains that are distributed to shareholders. However, the Fund’s failure to qualify as a regulated investment company would result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

For federal income tax purposes, distributions of investment income are generally taxable to you as ordinary income. Taxes on distributions of capital gains generally are determined by how long the Portfolio owned the investments that generated them, rather than how long you have owned your Fund shares. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before your investment (and thus were included in the price you paid for your shares). Distributions may also be subject to state and local taxes and are taxable whether you receive them in cash or reinvest them in additional shares. Distributions of net capital gains (that is, the excess of net long-term capital gains over net short-term capital losses) from the sale of investments that the Portfolio owned for more than one year that are properly designated by the Fund as capital gains dividends generally will be taxable to you as long-term capital gains. For individual taxpayers, long-term capital gain rates have been temporarily reduced--in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets--for taxable years beginning before January 1, 2011. Distributions of gains from investments that the Portfolio owned for one year or less generally will be taxable to you as ordinary income. For the taxable years beginning before January 1, 2011, distributions of investment income designated by the Fund as derived from “qualified dividend income” are taxed at the rates applicable to long-term capital gain, provided holding period and other requirements are met by both the shareholder and the Fund.

Financial Highlights

The Financial Highlights table is intended to help you understand the Fund’s Class R Shares financial performance since inception. Certain information reflects financial results for a single share of the Class R Shares. The total return in the table represents the rate that an investor would have earned (or lost) on an investment in the Fund’s Class R Shares (assuming reinvestment of all dividends and distributions). This information has been audited by_________, whose report, along with the Fund’s financial statements, is included in the Fund’s annual report, which is available upon request. The financial information included in this table should be read in conjunction with the financial statements incorporated by reference in the Statement of Additional Information.

For more information about STATE STREET EQUITY 500 INDEX FUND:

The SAI and the Fund’s annual and semi-annual reports are available, without charge, upon request. Shareholders in the Fund may make inquiries to the Fund to receive such information by calling (877) 521-4083 or the customer service center at the telephone number shown in the accompanying contract prospectus, if applicable. The Fund does not have an Internet website.

SSgA FUNDS MANAGEMENT, INC.

State Street Financial Center

One Lincoln Street

Boston, Massachusetts 02111

The State Street Institutional Investment Trust’s Investment Company Act File Number is 811-09819.

STATE STREET INSTITUTIONAL INVESTMENT TRUST

_______________

STATE STREET EQUITY 500 INDEX FUND (STBIX)

SERVICE SHARES

_______________

PROSPECTUS DATED APRIL__, 2010

_______________

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE. THIS FUND OFFERS THREE CLASSES OF SHARES: SERVICE CLASS, R CLASS AND ADMINISTRATIVE CLASS. THIS PROSPECTUS COVERS ONLY THE SERVICE CLASS.

AN INVESTMENT IN THE STATE STREET EQUITY 500 INDEX FUND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY.

Fund Summary
Other Investment Considerations and Risks
Management and Organization
Shareholder Information
Portfolio Holdings Disclosure
Distribution Servicing Plan and Payments to Financial Intermediaries
Dividends, Distributions and Tax Considerations
Financial Highlights

Fund Summary

Investment Objective

The Fund’s investment objective is to replicate as closely as possible, before expenses, the performance of the Standard & Poor’s 500 Index (the “S&P 500” or the “Index”).

Fees and Expenses of the Fund

The table describes the fees and expenses that you may pay if you buy and hold Service Shares of the Fund. As a shareholder in the State Street Equity 500 Index Portfolio (the “Equity 500 Index Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.045%
Distribution (12b-1) Fees	0.25%
Other Expenses	___%
Total Annual Fund Operating Expenses	___%

(1)	Amounts reflect the total expenses of the corresponding Portfolio of the State Street Master Funds and the Fund.

Example

This Example is intended to help you compare the cost of investing in the Fund’s Service Shares with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund’s Service Shares for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, that all dividends and distributions are reinvested, and that the Fund’s Service Shares’ operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

1 YEAR	3 YEARS	5 YEARS	10 YEARS
$___	$___	$___	$___

Portfolio Turnover

Principal Investment Strategies

Principal Risks

General risks associated with the Fund’s and Portfolio’s investment policies and investment strategies are discussed below.

·	Stock values could decline generally or could under-perform other investments.

Master/Feeder Structure Risk . Unlike a traditional mutual fund that invests directly in securities, the Fund pursues its objective by investing substantially all of its assets in the Master Portfolio with substantially the same investment objectives, policies and restrictions. The ability of the Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of the Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the corresponding Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio. The Adviser also serves as investment adviser to the Portfolio. Therefore, conflicts may arise as the Adviser fulfills its fiduciary responsibilities to the Fund and its corresponding Portfolio. For example, the Adviser may have an economic incentive to maintain the Fund’s investment in the Portfolio at a time when it might otherwise choose not to do so.

Performance

The bar chart below shows the performance of the Fund’s Service Shares during the Fund’s complete calendar years since inception. The chart provides some indication of the risks of investing in the Fund’s Service Shares by showing changes in the Service Shares’ performance from year to year. Please keep in mind that past performance does not necessarily indicate how the Fund’s Service Shares will perform in the future. Additionally, the performance information prior to March 10, 2003, the inception date for Service Shares, is that of Administrative Shares of the Fund, which incur lower expenses and typically experience higher returns than the Service Shares. The primary difference in expenses is the lower distribution (12b-1) fee of 0.15% for Administrative Shares compared to 0.25% for Service Shares on an annual basis. The Administrative Shares’ inception date was April 18, 2001.

State Street Equity 500 Index Fund

Service Shares

Total Return For The Calendar Years

Ended December 31

BAR CHART:

2002:	-22.31%
2003:	28.33%
2004:	10.51%
2005:	4.56%
2006:	15.41%
2007:	5.16%
2008:	-36.93%
2009:	___%

During the period shown in the bar chart, the highest return for a quarter was ___% (quarter ended ___) and the lowest return for a quarter was ___% (quarter ended ___ ).

Average Annual Total Returns

For the Periods Ended December 31, 2009

Service Shares

The information in the following table gives some indication of the risks of an investment in the Fund’s Service Shares by comparing the Fund’s Service Shares performance to the performance of the S&P 500 over various periods of time.

The Fund’s Service Shares’ after-tax returns listed below are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Additionally, actual after-tax returns depend on an investor’s tax situation and may differ from those shown below, and after-tax returns are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. Additionally, the following performance information prior to March 10, 2003, the inception date for Service Shares, is that of Administrative Shares of the Fund, which incur lower expenses and typically experience higher returns than the Service Shares. The Administrative Shares’ inception date was April 18, 2001.

	PAST 1-YEAR	PAST 5-YEAR	SINCE THE INCEPTION DATE OF THE FUND (ANNUALIZED)
State Street Equity 500 Index Fund
Return Before Taxes	___%	___%	___%
Return After Taxes on Distributions	___%	___%	___%
Return After Taxes on Distributions and Sale of Fund Shares	___%	___%	___%
S&P 500(reflects no deduction for expenses of taxes)	___%	___%	___%

__________

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

John A. Tucker has been a Portfolio Manager for the Portfolio since 2007. Karl Schneider has been a Portfolio Manager for the Portfolio since 2002.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account	$25,000,000
To add to an existing account	No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

BY MAIL:

State Street Equity 500 Index Fund

P.O. Box 5493

Boston, MA 02206

BY OVERNIGHT:

State Street Equity 500 Index Fund

200 Clarendon Street

Boston, MA 02116

BY TELEPHONE:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

Other Investment Considerations and Risks

Portfolio Holdings Disclosure

The Fund’s portfolio holdings disclosure policy is described in the Statement of Additional Information.

Management and Organization

The Equity 500 Index Fund offers three classes of shares: Administrative Shares, Service Shares and Class R Shares. Only the Service Shares of the Fund are discussed in this prospectus.

The Adviser . State Street Global Advisors (“SSgA”) is the investment management group of State Street Corporation, a publicly held bank holding company, and includes the Adviser, SSgA FM, a wholly-owned subsidiary. SSgA is one of the world’s largest institutional money managers, and uses quantitative and traditional techniques to manage approximately $1.91 trillion as of December 31, 2009 in investment programs and portfolios for institutional and individual investors. SSgA FM, as the investment adviser to the Fund and the Portfolio, is registered with the Securities and Exchange Commission (“SEC”) under the Investment Advisers Act of 1940 as amended. SSgA FM had approximately $168.4 billion in assets under management at December 31, 2009. The Fund has entered into an investment advisory agreement with the Adviser pursuant to which the Adviser will manage the Fund’s assets directly, for compensation paid at an annual rate of 0.10% of the Fund’s average daily net assets, in the event that the Fund were to cease investing substantially all of its assets in the Portfolio. The Adviser does not receive any fees from the Fund under that agreement so long as the Fund continues to invest substantially all of its assets in the Portfolio or in another investment company. The Adviser places all orders for purchases and sales of the Portfolio’s investments.

John A. Tucker, CFA

Karl Schneider

The Adviser’s principal address is State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111.

The Distributor . State Street Global Markets, LLC serves as the Fund’s distributor (the “Distributor”) pursuant to the Distribution Agreement between the Distributor and the Trust.

Shareholder Information

Determination of Net Asset Value . The Fund determines its net asset value (“NAV”) per share once each business day as of the close of regular trading on the NYSE. The NAV per share is based on the market value of the investments held in the Fund. The NAV of the Fund’s Service shares is calculated by dividing the value of the assets of the Fund attributable to its Service Shares less the liabilities of the Fund attributable to its Service Shares by the number of Service Shares outstanding. The Fund values each security or other investment pursuant to guidelines adopted by the Board of Trustees. Securities or other investments may be valued at fair value, as determined in good faith and pursuant to procedures approved by the Portfolio’s Board of Trustees, under certain limited circumstances. For example, fair value pricing may be used when market quotations are not readily available or reliable, such as when (i) trading for a security is restricted; or (ii) a significant event, as determined by the Adviser, that may affect the value of one or more securities or other investments held by the Fund occurs after the close of a related exchange but before the determination of the Fund’s NAV. Attempts to determine the fair value of securities or other investments introduce an element of subjectivity to the pricing of securities or other investments. As a result, the price of a security or other investment determined through fair valuation techniques may differ from the price quoted or published by other sources and may not accurately reflect the price the Fund would have received had it sold the investment. To the extent that the Fund invests in the shares of other registered open-end investment companies that are not traded on an exchange (mutual funds), such shares are valued at their published net asset values per share as reported by the funds. The prospectuses of these funds explain the circumstances under which the funds will use fair value pricing and the effects of using fair value pricing.

In accordance with certain federal regulations, the Trust is required to obtain, verify and record information that identifies each entity that applies to open an account. For this reason, when you open (or change ownership of ) an account, the Trust will request certain information, including your name, address and taxpayer identification number, which will be used to verify your identity. If you are unable to provide sufficient information to verify your identity, the Trust will not open an account for you. As required by law, the Trust may employ various procedures, such as comparing your information to fraud databases or requesting additional information and documentation from you, to ensure that the information supplied by you is correct. The Trust reserves the right to reject any purchase order for any reason, including failure to provide the Trust with information necessary to confirm your identity as required by law.

Policies to Prevent Market Timing . Frequent purchases and redemptions of Fund shares may present risks for other shareholders of the Fund, which may include, among other things, interference in the efficient management of the Fund’s portfolio, dilution in the value of Fund shares held by long-term shareholders, increased brokerage and administrative costs and forcing the Fund to hold excess levels of cash.

The Fund reserves the right in its discretion to reject any purchase, in whole or in part including, without limitation, by a person whose trading activity in Fund shares the Adviser believes could be harmful to the Fund. The Fund may decide to restrict purchase activity in its shares based on various factors, including, without limitation, whether frequent purchase and sale activity will disrupt portfolio management strategies and adversely affect performance. There can be no assurance that the Fund, the Adviser or State Street will identify all frequent purchase and sale activity affecting the Fund.

Distribution/Servicing (Rule 12b-1) Plan

The Fund has adopted a distribution plan under which the Fund may compensate its distributor (or others) for services in connection with the distribution of the Fund’s Service Shares and for services provided to Fund shareholders. The plan calls for payments at an annual rate (based on average daily net assets) of 0.25% of the Fund’s net assets attributable to its Service Shares. Because these fees are paid out of the assets of the Fund attributable to its Service Shares, on an ongoing basis, they will increase the cost of your investment and may cost you more over time than paying other types of sales charges.

Additional Payments to Financial Intermediaries

Dividends, Distributions and Tax Considerations

Income dividends and capital gains distributions of the Fund will be declared and paid at least annually.

The Fund intends to elect to be treated and qualify each year as a regulated investment company. A regulated investment company is generally not subject to tax at the corporate level on income and gains that are distributed to shareholders. However, the Fund’s failure to qualify as a regulated investment company would result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

For federal income tax purposes, distributions of investment income are generally taxable to you as ordinary income. Taxes on distributions of capital gains generally are determined by how long the Portfolio owned the investments that generated them, rather than how long you have owned your Fund shares. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before your investment (and thus were included in the price you paid for your shares). Distributions may also be subject to state and local taxes and are taxable whether you receive them in cash or reinvest them in additional shares. Distributions of net capital gains (that is, the excess of net long-term capital gains over net short-term capital losses) from the sale of investments that the Portfolio owned for more than one year that are properly designated by the Fund as capital gains dividends generally will be taxable to you as long-term capital gains. For individual taxpayers, long-term capital gain rates have been temporarily reduced -- in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets -- for taxable years beginning before January 1, 2011. Distributions of gains from investments that the Portfolio owned for one year or less generally will be taxable to you as ordinary income. For the taxable years beginning before January 1, 2011, distributions of investment income designated by the Fund as derived from “qualified dividend income” are taxed at the rates applicable to long-term capital gain, provided holding period and other requirements are met by both the shareholder and the Fund.

Financial Highlights

The Financial Highlights table is intended to help you understand the Fund’s Service Shares financial performance for the past 5 years. Certain information reflects financial results for a single share of the Service Shares. The total return in the table represents the rate that an investor would have earned (or lost) on an investment in the Fund’s Service Shares (assuming reinvestment of all dividends and distributions). This information has been audited by________, whose report, along with the Fund’s financial statements, is included in the Fund’s annual report, which is available upon request. The financial information included in this table should be read in conjunction with the financial statements incorporated by reference in the Statement of Additional Information.

For more information about STATE STREET EQUITY 500 INDEX FUND:

The SAI and the Fund’s annual and semi-annual reports are available, without charge, upon request. Shareholders in the Fund may make inquiries to the Fund to receive such information by calling (877) 521-4083 or the customer service center at the telephone number shown in the accompanying contract prospectus, if applicable. The Fund does not have an Internet website.

SSgA FUNDS MANAGEMENT, INC .

State Street Financial Center

One Lincoln Street

Boston, Massachusetts 02111

The State Street Institutional Investment Trust’s Investment Company Act File Number is 811-09819.

STATE STREET INSTITUTIONAL INVESTMENT TRUST

_______________

STATE STREET EQUITY 400 INDEX FUND

_______________

PROSPECTUS DATED APRIL__, 2010

_______________

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

AN INVESTMENT IN THE STATE STREET EQUITY 400 INDEX FUND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY.

Fund Summary
Other Investment Considerations and Risks
Management and Organization
Shareholder Information
Portfolio Holdings Disclosure
Distribution Servicing Plan and Payments to Financial Intermediaries
Dividends, Distributions and Tax Considerations
Financial Highlights

Fund Summary

Investment Objective

The Fund’s investment objective is to replicate as closely as possible, before expenses, the performance of the Standard & Poor’s MidCap 400 Index (the “S&P MidCap 400” or the “Index”). The Fund seeks to achieve its investment objective by investing substantially all of its investable assets in the State Street Equity 400 Index Portfolio (the “Equity 400 Index Portfolio” or sometimes referred to in context as the “Portfolio”) of the State Street Master Funds that has the same investment objective as, and investment policies that are substantially similar to those of, the Fund. In reviewing the investment objective and policies of the Fund below, you should assume that the investment objective and policies of the Portfolio are the same in all material respects as those of the Fund. There is no assurance that the Fund will achieve its investment objective.

Fees and Expenses of the Fund

The table describes the estimated fees and expenses that you may pay if you buy and hold shares of the Fund. As a shareholder in the State Street Equity 400 Index Portfolio (the “Equity 400 Index Portfolio” or sometimes referred to in context as the “Portfolio”), the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Shareholder Fees

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.08%
Distribution (12b-1) Fees	0.25%
Other Expenses (2)	___ %
Total Annual Fund Operating Expenses	___ %

____________

(1)	Amounts reflect total estimated expenses for the Portfolio and the Fund.

(2)	Other Expenses are based on estimated amounts for the current fiscal year.

Example

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

1 YEAR	3 YEARS
$__	$__

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). As a shareholder of the Portfolio the Fund bears its ratable share of the transaction costs associated with the portfolio turnover of the Portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. The Fund’s portfolio turnover rate has been omitted because the Fund had not commenced investment operations as of the date of this Prospectus.

Principal Investment Strategies

The Portfolio uses a passive management strategy designed to track the S&P MidCap 400. The Index is a well-known stock market index that includes common stocks of 400 mid-sized companies from several industrial sectors representing a significant portion of the market value of all stocks publicly traded in the United States.

The Portfolio is not managed according to traditional methods of “active” management, which involve the buying and selling of securities based upon economic, financial and market analysis and investment judgment. Instead, the Portfolio, using a “passive” or “indexing” investment approach, attempts to replicate, before expenses, the performance of the S&P MidCap 400.

The Portfolio generally intends to invest in all of the stocks comprising the Index in proportion to their weightings in the Index. However, under various circumstances, it may not be possible or practicable to purchase all 400 stocks in those weightings. In those circumstances, the Portfolio may purchase a sample of the stocks in the Index in proportions expected by the Adviser to match generally the performance of the Index as a whole. In addition, from time to time stocks are added to or removed from the Index. The Portfolio may sell stocks that are represented in the Index, or purchase stocks that are not yet represented in the Index, in anticipation of their removal from or addition to the Index. Under normal market conditions, the Portfolio will not invest less than 80% of its total assets in stocks in the Index. Shareholders will receive 60 days’ notice prior to a change in the 80% investment policy.

Principal Risks

Stock values could decline generally or could under-perform other investments.

Because the S&P MidCap 400 includes stocks of mainly mid-capitalization (“mid-cap”) companies, the Portfolio’s investments consist mainly of stocks of mid-cap companies. Returns on investments in mid-cap stocks could be more volatile than, or trail the returns on, investments in larger or smaller capitalization (“large-cap” and “small-cap,” respectively) U.S. stocks.

Mid-cap companies may be more likely than large-cap companies to have relatively limited product lines, markets or financial resources, or depend on a few key employees.

The Portfolio’s return may not match the return of the Index for a number of reasons. For example, the return on the securities and other investments selected by the Adviser may not correlate precisely with the return on the Index. The Portfolio incurs a number of operating expenses not applicable to the Index, and incurs costs in buying and selling securities. The Portfolio may not be fully invested at times, either as a result of cash flows into the Portfolio or reserves of cash held by the Portfolio to meet redemptions. The return on the sample of securities purchased by the Portfolio, or futures or other derivative positions taken by the Portfolio, to replicate the performance of the Index may not correlate precisely with the return on the Index.

Master/Feeder Structure Risk . Unlike a traditional mutual fund that invests directly in securities, the Fund pursues its objective by investing substantially all of its assets in the Master Portfolio with substantially the same investment objectives, policies and restrictions. The ability of the Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of the Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the corresponding Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio. The Adviser also serves as investment adviser to the Portfolio. Therefore, conflicts may arise as the Adviser fulfills its fiduciary responsibilities to the Fund and its corresponding Portfolio. For example, the Adviser may have an economic incentive to maintain the Fund’s investment in the Portfolio at a time when it might otherwise choose not to do so.

Performance

Performance information for the Fund has been omitted because the Fund had not commenced investment operations as of the date of this Prospectus.

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account	$25,000,000
To add to an existing account	No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

BY MAIL:

State Street Equity 400 Index Fund

P.O. Box 5493

Boston, MA 02206

BY OVERNIGHT:

State Street Equity 400 Index Fund

200 Clarendon Street

Boston, MA 02116

BY TELEPHONE:

Through Brokers, Banks and Other Financial Intermediaries . If you wish to purchase or redeem Fund shares through a broker, bank or other financial intermediary, please contact that financial intermediary directly. Your financial intermediary may have an earlier cut-off time for the submission of purchase or redemption orders or may be closed at times when the Fund is open.

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

Other Investment Considerations and Risks

The S&P MidCap 400. The S&P MidCap 400 is a well-known stock market index that includes common stocks of 400 companies from several industrial sectors representing a large cross-section of mid-cap stocks publicly traded in the United States, most of which are listed on the New York Stock Exchange, Inc. (the “NYSE”). Unlike the S&P 500, which is designed to represent the performance of the large-cap sector of the U.S. securities market, the S&P MidCap 400 is designed to represent the performance of the mid-cap sector of the U.S. securities market. Stocks in the S&P MidCap 400 are weighted according to their market capitalizations (i.e., the number of shares outstanding multiplied by the stock’s current price). The companies chosen for the S&P MidCap 400 generally have market values between $1 billion and $4 billion, depending upon current equity market valuations. (Stocks in the S&P MidCap 400 will not simultaneously be listed in the S&P 500.) The composition of the S&P MidCap 400 is determined by Standard & Poor’s(R) and is based on such factors as the market capitalization and trading activity of each stock and its adequacy as a representation of stocks in a particular industry group, and may be changed from time to time. “Standard & Poor’s(R),” “S&P,” “S&P MidCap 400,” “Standard & Poor’s 400” and “400” are trademarks of The McGraw-Hill Companies, Inc. and have been licensed for use by the Fund and the Portfolio. The Fund and the Portfolio are not sponsored, endorsed, sold or promoted by S&P, and S&P makes no representation regarding the advisability of investing in the Fund or the Portfolio.

Index Futures Contracts and Related Options. The Portfolio may buy and sell futures contracts on the S&P MidCap 400 and options on those futures contracts. An “index futures” contract is a contract to buy or sell units of an index at an agreed price on a specified future date. Depending on the change in value of the Index between the time when the Portfolio enters into and closes out an index future or option transaction, the Portfolio realizes a gain or loss. Options and futures transactions involve risks. For example, it is possible that changes in the prices of futures contracts on the Index will not correlate precisely with changes in the value of the Index. In those cases, use of futures contracts and related options might decrease the correlation between the return of the Portfolio and the return of the Index. In addition, the Portfolio incurs transaction costs in entering into, and closing out, positions in futures contracts and related options. These costs typically have the effect of reducing the correlation between the return of the Portfolio and the return of the Index. Because the secondary market for futures contracts and options may be illiquid, the Portfolio may have to hold a contract or option when the Adviser would otherwise have sold it, or it may only be able to sell at a price lower than what the Adviser believes is the fair value of the contract or option, thereby potentially reducing the return of the Portfolio.

Portfolio Holdings Disclosure

The Fund’s portfolio holdings disclosure policy is described in the Statement of Additional Information.

Management and Organization

The Fund and the Portfolio . The State Street Equity 400 Index Fund (the “Fund”) is a series of the State Street Institutional Investment Trust (the “Trust”), which is an open-end management investment company organized as a business trust under the laws of the Commonwealth of Massachusetts.

The Adviser . State Street Global Advisors (“SSgA”) is the investment management group of State Street Corporation, a publicly held bank holding company, and includes the Adviser, SSgA FM, a wholly-owned subsidiary. SSgA is one of the world’s largest institutional money managers, and uses quantitative and traditional techniques to manage approximately $1.91 trillion as of December 31, 2009 in investment programs and portfolios for institutional and individual investors. SSgA FM, as the investment adviser to the Fund and the Portfolio, is registered with the Securities and Exchange Commission (“SEC”) under the Investment Advisers Act of 1940, as amended. SSgA FM had approximately $168.4 billion in assets under management at December 31, 2009. The Fund has entered into an investment advisory agreement with the Adviser pursuant to which the Adviser will manage the Fund’s assets directly, for compensation paid at an annual rate of 0.10% of the Fund’s average daily net assets, in the event that the Fund were to cease investing substantially all of its assets in the Portfolio. The Adviser does not receive any fees from the Fund under that agreement so long as the Fund continues to invest substantially all of its assets in the Portfolio or in another investment company. The Adviser places all orders for purchases and sales of the Portfolio’s investments.

A summary of the factors considered by the Board of Trustees in connection with the renewal of the investment advisory agreement for the Fund will be available in the Fund’s annual report or semi-annual report, as applicable, after the Fund commences operations.

The Adviser’s principal address is State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111.

The Distributor . State Street Global Markets, LLC serves as the Fund’s distributor (the “Distributor”) pursuant to the Distribution Agreement between the Distributor and the Trust.

Shareholder Information

Determination of Net Asset Value . The Fund determines its net asset value (“NAV”) per share once each business day as of the close of regular trading on the NYSE. The NAV per share is based on the market value of the securities held in the Fund. The NAV per share is calculated by dividing the assets less liabilities of the Fund by the number of shares outstanding. The Fund values each security pursuant to guidelines adopted by the Board of Trustees. Securities may be valued at fair value, as determined in good faith and pursuant to procedures approved by the Portfolio’s Board of Trustees, under certain limited circumstances. For example, fair value pricing may be used when market quotations are not readily available or reliable, such as when (i) trading for a security is restricted; or (ii) a significant event, as determined by the Adviser, that may affect the value of one or more securities held by the Fund occurs after the close of a related exchange but before the determination of the Fund’s NAV. Attempts to determine the fair value of securities introduce an element of subjectivity to the pricing of securities. As a result, the price of a security determined through fair valuation techniques may differ from the price quoted or published by other sources and may not accurately reflect the price the Fund would have received had it sold the investment. To the extent that the Fund invests in the shares of other registered open-end investment companies that are not traded on an exchange (mutual funds), such shares are valued at their published net asset values per share as reported by the funds. The prospectuses of these funds explain the circumstances under which the funds will use fair value pricing and the effects of using fair value pricing.

Purchasing Shares . Investors pay no sales load to invest in this Fund. The price for Fund shares is the NAV per share. Orders will be priced at the NAV next calculated after the order is accepted by the Fund.

The minimum initial investment in the Fund is $25 million, although the Adviser may waive the minimum in its discretion. There is no minimum subsequent investment. The Fund intends to be as fully invested as is practicable; therefore, investments must be made either in Federal Funds (i.e., monies credited to the account of the Fund’s custodian bank by a Federal Reserve Bank) or securities (“in-kind”) acceptable to the Adviser. (Please consult your tax adviser regarding in-kind transactions.) The Fund reserves the right to cease accepting investments at any time or to reject any purchase order.

In accordance with certain federal regulations, the Trust is required to obtain, verify and record information that identifies each entity who applies to open an account. For this reason, when you open (or change ownership of) an account, the Trust will request certain information, including your name, address and taxpayer identification number, which will be used to verify your identity. If you are unable to provide sufficient information to verify your identity, the Trust will not open an account for you. As required by law, the Trust may employ various procedures, such as comparing your information to fraud databases or requesting additional information and documentation from you, to ensure that the information supplied by you is correct. The Trust reserves the right to reject any purchase for any reason, including failure to provide the Trust with information necessary to confirm your identity as required by law.

Policies to Prevent Market Timing . Frequent purchases and redemptions of Fund shares may present risks for other shareholders of the Fund, which may include, among other things, interference in the efficient management of the Fund’s portfolio, dilution in the value of Fund shares held by long-term shareholders, increased brokerage and administrative costs and forcing the Fund to hold excess levels of cash.

The Fund is intended as a long-term investment. Therefore, the Trust’s Board of Trustees has adopted policies and procedures designed to detect and prevent inappropriate short-term trading activity that is harmful to the Fund. Because most of the interests in the Fund are held by investors indirectly through one or more financial intermediaries, the Fund does not generally have information about the identity of those investors or about transactions effected by those investors. Rather, the Fund and its service providers periodically review cash inflows and outflows from and to those intermediaries in an attempt to detect inappropriate trading activity by investors holding shares through those intermediaries. The Fund may not be able to determine whether trading by an investor holding shares through a financial intermediary is engaged in trading activity in the Fund’s shares that may be harmful to the Fund or its shareholders.

The Fund reserves the right in its discretion to reject any purchase, in whole or in part including, without limitation, by a person whose trading activity in Fund shares the Adviser believes could be harmful to the Fund. The Fund may decide to restrict purchase activity in its shares based on various factors, including, without limitation, whether frequent purchase and sale activity will disrupt portfolio management strategies and adversely affect performance. There can be no assurance that the Fund, the Adviser or State Street will identify all frequent purchase and sale activity affecting the Fund.

Distribution/Servicing (Rule 12b-1) Plan

The Fund has adopted a distribution plan under which the Fund may compensate its distributor (or others) for services in connection with the distribution of the Fund’s shares and for services provided to Fund shareholders. The plan calls for payments at an annual rate (based on average daily net assets) of 0.25%. Because these fees are paid out of the Fund’s assets on an ongoing basis, they will increase the cost of your investment and may cost you more over time than paying other types of sales charges.

Additional Payments to Financial Intermediaries

Dividends, Distributions and Tax Considerations

Income dividends and capital gains distributions of the Fund will be declared and paid at least annually.

The Fund intends to elect to be treated and qualify each year as a regulated investment company. A regulated investment company is generally not subject to tax at the corporate level on income and gains that are distributed to shareholders. However, the Fund’s failure to qualify as a regulated investment company would result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

For federal income tax purposes, distributions of investment income are generally taxable to you as ordinary income. Taxes on distributions of capital gains generally are determined by how long the Portfolio owned the investments that generated them, rather than how long you have owned your Fund shares. Distributions are taxable to you even if they are paid from income or gains earned by the Fund before your investment (and thus were included in the price you paid for your shares). Distributions may also be subject to state and local taxes and are taxable whether you receive them in cash or reinvest them in additional shares. Distributions of net capital gains (that is, the excess of net long-term capital gains over net short-term capital losses) from the sale of investments that the Portfolio owned for more than one year that are properly designated by the Fund as capital gains dividends generally will be taxable to you as long-term capital gains. For individual taxpayers long-term capital gain rates have been temporarily reduced--in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets--for taxable years beginning before January 1, 2011. Distributions of gains from investments that the Portfolio owned for one year or less generally will be taxable to you as ordinary income. For the taxable years beginning before January 1, 2011, distributions of investment income designated by the Fund as derived from “qualified dividend income” are taxed at the rates applicable to long-term capital gain, provided holding period and other requirements are met by both the shareholder and the Fund.

Financial Highlights

The Financial Highlights table is not presented because the Fund had not commenced operations as of the date of this Prospectus.

For more information about STATE STREET EQUITY 400 INDEX FUND:

The Fund’s statement of additional information (SAI) includes additional information about the Fund and is incorporated by reference into this document. Additional information about the Fund’s investments will be available in the Fund’s annual and semi-annual reports to shareholders. In the Fund’s annual report, you will find a discussion of the market conditions and investment strategies that significantly affected the Fund’s performance during its last fiscal year.

The SAI and the Fund’s annual and semi-annual reports will be available, without charge, upon request. Shareholders in the Fund may make inquiries to the Fund to receive such information by calling (877) 521-4083. The Fund does not have an Internet website.

SSgA FUNDS MANAGEMENT, INC.

State Street Financial Center

One Lincoln Street

Boston, Massachusetts 02111

The State Street Institutional Investment Trust’s Investment Company Act File Number is 811-09819.

STATE STREET INSTITUTIONAL INVESTMENT TRUST

_______________

STATE STREET EQUITY 2000 INDEX FUND

_______________

PROSPECTUS DATED APRIL __, 2010

_______________

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

AN INVESTMENT IN THE STATE STREET EQUITY 2000 INDEX FUND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY.

Fund Summary
Other Investment Considerations and Risks
Management and Organization
Shareholder Information
Portfolio Holdings Disclosure
Distribution Servicing Plan and Payments to Financial Intermediaries
Dividends, Distributions and Tax Considerations
Financial Highlights

Fund Summary

Investment Objective

The Fund’s investment objective is to replicate as closely as possible, before expenses, the performance of the Russell 2000 Index.

Fees and Expenses of the Fund

The table describes the estimated fees and expenses that you may pay if you buy and hold shares of the Fund. As a shareholder in the Portfolio, the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Shareholder Fees

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.10%
Distribution (12b-1) Fees	0.25%
Other Expenses (2)	___ %
Total Annual Fund Operating Expenses	___%
Less Fee Waivers and/or Reimbursements (3)
Total Annual Fund Operating Expenses After Fee waivers and Expense Reimbursements	0.20%

____________

(1)	Amounts reflect total estimated expenses for the Portfolio and the Fund.

(2)	Other Expenses are based on estimated amounts for the current fiscal year.

(3)

Through December 31, 2011, the total annualized operating expenses of the Fund are not expected to exceed 0.20% (excluding non-recurring account fees and extraordinary expenses of the Fund or Portfolio) because the Adviser has contractually agreed to: (i) waive fees and/or reimburse certain operating expenses of the Portfolio in amounts necessary to limit the total annual operating expenses of the Portfolio to 0.15% and (ii) waive fees and/or reimburse certain operating expenses of the Fund in amounts necessary to limit the total annual operating expenses of the Fund to 0.05% (excluding pass-through expenses from the Portfolio). Prior to December 31, 2011, these contractual waivers and reimbursements may not be terminated without the approval of the Board of Trustees of the Fund and/or Portfolio, as applicable.

Example

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

1 YEAR	3 YEARS
$___	$___

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). As a shareholder of the Portfolio the Fund bears its ratable share of the transaction costs associated with the portfolio turnover of the Portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. The Fund’s portfolio turnover rate has been omitted because the Fund had not commenced investment operations as of the date of this Prospectus.

Principal Investment Strategies

The Fund seeks to achieve its investment objective by investing substantially all of its investable assets in a corresponding portfolio (the “Portfolio”) of the State Street Master Funds that has the same investment objective as, and investment policies that are substantially similar to those of, the Fund. In reviewing the investment policies of the Fund below, you should assume that the investment policies of the Portfolio are the same in all material respects as those of the Fund. There is no assurance that the Fund will achieve its investment objective.

The Portfolio uses a management strategy designed to track the performance of the Russell 2000 Index. The Russell 2000 Index is one of the most widely accepted benchmarks of U.S. small capitalization stock market total return. It includes the smallest 2,000 securities in the Russell 3000(R) Index.

The Portfolio, using an “indexing” investment approach, attempts to replicate, before expenses, the performance of the Russell 2000 Index.

The Portfolio may invest in all of the stocks comprising the Russell 2000 Index in proportion to their weightings in the Index. However, under various circumstances, it may not be possible or practicable to purchase all of those stocks in those weightings. In those circumstances, the Portfolio may purchase a representative sample of the stocks in the Index in proportions expected by the Adviser to replicate generally the performance of the Index as a whole. In addition, from time to time stocks are added to or removed from the Index. The Portfolio may sell stocks that are represented in the Index, or purchase stocks that are not yet represented in the Index, in anticipation of their removal from or addition to the Index. Under normal market conditions, the Portfolio will not invest less than 80% of its total assets in stocks in the Index. Shareholders will receive 60 days’ notice prior to a change in the 80% investment policy.

In addition, the Portfolio may at times purchase or sell futures contracts on the Index, or on securities, or options on those futures, in lieu of investing directly in the stocks making up the Index. The Portfolio might do so, for example, in order to increase its investment exposure pending investment of cash in the stocks comprising the Index or to reduce its investment exposure in situations where it intends to sell a portion of the stocks in its portfolio but the sale has not yet been completed. The Portfolio may also enter into other derivatives transactions, including the use of options or swap transactions, to assist in attempting to replicate the performance of the Index. The Portfolio may also, to the extent permitted by applicable law, invest in shares of other mutual funds whose investment objectives and policies are similar to those of the Portfolio, including other mutual funds and exchange-traded funds advised or sponsored by the Adviser or its affiliates.

Principal Risks

Stock Market Risk. Stock values could decline generally or could under-perform other investments.

Small-Cap Stock Risk. Returns on investments in stocks of small U.S. companies could be more volatile than, or trail the returns on, investments in stocks of larger or medium capitalization companies.

Small companies may be more likely than mid-cap and large-cap companies to have relatively limited product lines, markets or financial resources, or depend on a few key employees.

Tracking Error Risk. The Portfolio’s return may not match the return of the Russell 2000 Index for a number of reasons. For example, the return on the securities and other investments selected by the Adviser may not correlate precisely with the return on the Index. The Portfolio incurs a number of operating expenses not applicable to the Index, and incurs costs in buying and selling securities. The Portfolio may not be fully invested at times, either as a result of cash flows into the Portfolio or reserves of cash held by the Portfolio to meet redemptions. The return on the sample of securities purchased by the Portfolio, or futures or other derivative positions taken by the Portfolio, to replicate the performance of the Index may not correlate precisely with the return on the Index.

Derivatives Risk . Futures, options and other derivative transactions typically involve leverage and may be highly volatile. It is possible that a derivative transaction will result in a loss greater than the principal amount invested, and the Portfolio may not be able to close out a derivative transaction at a favorable time or price.

Master/Feeder Structure Risk . Unlike a traditional mutual fund that invests directly in securities, the Fund pursues its objective by investing substantially all of its assets in the Master Portfolio with substantially the same investment objectives, policies and restrictions. The ability of the Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of the Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the corresponding Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio. The Adviser also serves as investment adviser to the Portfolio. Therefore, conflicts may arise as the Adviser fulfills its fiduciary responsibilities to the Fund and its corresponding Portfolio. For example, the Adviser may have an economic incentive to maintain the Fund’s investment in the Portfolio at a time when it might otherwise choose not to do so.

Performance

Performance information for the Fund has been omitted because the Fund had not commenced investment operations as of the date of this Prospectus.

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account	$25,000,000
To add to an existing account	No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

BY MAIL:

State Street Equity 2000 Index Fund

P.O. Box 5493

Boston, MA 02206

BY OVERNIGHT:

State Street Equity 2000 Index Fund

200 Clarendon Street

Boston, MA 02116

BY TELEPHONE:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

Other Investment Considerations and Risks

The following information supplements the principal investment strategies and risks described above under “Fund Summary.”

Changes in Policies. The Trust’s Board of Trustees may change the Fund’s investment strategies and other policies without shareholder approval, except as otherwise indicated. The Board of Trustees will not materially change the Fund’s investment objective without shareholder approval.

The Russell 2000 Index. The Russell 2000 Index is composed of 2,000 common stocks, which are selected by Frank Russell Company (“Russell”), based upon market capitalization. Each year on May 31 st , Russell ranks the 3,000 largest U.S. stocks by market capitalization in order to create the Russell 3000 Index, which represents approximately 98% of the total U.S. equity market. After the initial list of 3,000 eligible stocks is determined, the shares outstanding for each company are adjusted for corporate cross-ownership and large private holdings. The Russell 2000 Index is a subset of the Russell 3000 Index, representing the smallest 2,000 stocks of the Russell 3000 Index. The purpose of the Russell 2000 Index is to provide a comprehensive representation of the investable U.S. small-capitalization equity market. The inclusion of a stock in the Russell 2000 Index in no way implies that Russell believes the stock to be an attractive investment, nor is Russell a sponsor or in any way affiliated with the Fund or Portfolio. The securities in the Russell 2000 Index, most of which trade on the New York Stock Exchange (the “NYSE”) and Nasdaq, represent approximately 8% of the market value of all U.S. common stocks. The Russell 2000 Index only includes common stocks domiciled in the United States and its territories.

Index Futures Contracts and Related Options . The Portfolio may buy and sell futures contracts on the Russell 2000 Index and options on those futures contracts. An “index futures” contract is a contract to buy or sell units of an index at an agreed price on a specified future date. Depending on the change in value of the Index between the time when the Portfolio enters into and closes out an index future or option transaction, the Portfolio realizes a gain or loss. Options and futures transactions involve risks. For example, it is possible that changes in the prices of futures contracts on the Index will not correlate precisely with changes in the value of the Index. In those cases, use of futures contracts and related options might decrease the correlation between the return of the Portfolio and the return of the Index. In addition, the Portfolio incurs transaction costs in entering into, and closing out, positions in futures contracts and related options. These costs typically have the effect of reducing the correlation between the return of the Portfolio and the return of the Index. Because the secondary market for futures contracts and options may be illiquid, the Portfolio may have to hold a contract or option when the Adviser would otherwise have sold it, or it may only be able to sell at a price lower than what the Adviser believes is the fair value of the contract or option, thereby potentially reducing the return of the Portfolio.

Real Estate Investment Trusts . The Fund may invest in real estate investment trusts (“REITs”). REITs involve certain special risks in addition to those risks associated with investing in the real estate industry in general (such as possible declines in the value of real estate, lack of availability of mortgage funds or extended vacancies of property). Equity REITs may be affected by changes in the value of the underlying property owned by the REITs, while mortgage REITs may be affected by the quality of any credit extended. REITs are dependent upon management skills, are subject to heavy cash flow dependency, risks of default by borrowers, and self-liquidation. REITs are also subject to the possibilities of failing to qualify for tax-free pass-through of income under the Internal Revenue Code, and failing to maintain their exemptions from registration under the Investment Company Act of 1940, as amended (the “1940 Act”). Investing in REITs involves risks similar to those associated with investing in small capitalization companies. REITs may have limited financial resources, may trade less frequently and in limited volume and may be subject to more volatility than other investments.

Portfolio Holdings Disclosure

The Fund’s portfolio holdings disclosure policy is described in the Statement of Additional Information.

Management and Organization

The Fund and the Portfolio . The State Street Equity 2000 Index Fund (the “Fund”) is a mutual fund that seeks to provide an investment return matching, as closely as possible before expenses, the performance of the Russell 2000(R) Index (the “Russell 2000 Index” or the “Index”). The Fund is a separate, diversified series of the State Street Institutional Investment Trust (the “Trust”), which is an open-end management investment company organized as a business trust under the laws of the Commonwealth of Massachusetts.

The Adviser . State Street Global Advisors (“SSgA”) is the investment management group of State Street Corporation, a publicly held bank holding company, and includes the Adviser, SSgA FM, a wholly-owned subsidiary. SSgA is one of the world’s largest institutional money managers, and uses quantitative and traditional techniques to manage approximately $1.91 trillion as of December 31, 2009 in investment programs and portfolios for institutional and individual investors. SSgA FM, as the investment adviser to the Fund and the Portfolio, is registered with the Securities and Exchange Commission (“SEC”) under the Investment Advisers Act of 1940, as amended. SSgA FM had approximately $168.4 billion in assets under management at December 31, 2009. The Fund has entered into an investment advisory agreement with the Adviser, pursuant to which the Adviser will manage the Fund’s assets directly, for compensation paid at an annual rate of .10% of the Fund’s average daily net assets, in the event that the Fund were to cease investing substantially all of its assets in the Portfolio. The Adviser does not receive any fees from the Fund under that agreement so long as the Fund continues to invest substantially all of its assets in the Portfolio or in another investment company. The Adviser places all orders for purchases and sales of the Portfolio’s investments.

The Adviser’s principal address is State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111.

The Administrator, Custodian, Transfer Agent and Dividend Disbursing Agent . State Street Bank and Trust Company (“State Street “), a subsidiary of State Street Corporation, is the administrator, custodian, transfer agent and dividend disbursing agent for the Fund.

The Distributor . State Street Global Markets, LLC serves as the Fund’s distributor (the “Distributor”) pursuant to the Distribution Agreement between the Distributor and the Trust.

Shareholder Information

Determination of Net Asset Value . The Fund determines its net asset value (“NAV”) per share once each business day as of the close of regular trading on the NYSE. The NAV per share is based on the market value of the securities held in the Fund. The NAV per share is calculated by dividing the assets less liabilities of the Fund by the number of shares outstanding. The Fund values each security pursuant to guidelines adopted by the Board of Trustees. Securities may be valued at fair value, as determined in good faith and pursuant to procedures approved by the Portfolio’s Board of Trustees, under certain limited circumstances. For example, fair value pricing may be used when market quotations are not readily available or reliable, such as when (i) trading for a security is restricted; or (ii) a significant event, as determined by the Adviser, that may affect the value of one or more securities held by the Fund occurs after the close of a related exchange but before the determination of the Fund’s NAV. Attempts to determine the fair value of securities introduce an element of subjectivity to the pricing of securities. As a result, the price of a security determined through fair valuation techniques may differ from the price quoted or published by other sources and may not accurately reflect the price the Fund would have received had it sold the investment. To the extent that the Fund invests in the shares of other registered open-end investment companies that are not traded on an exchange (mutual funds), such shares are valued at their published net asset values per share as reported by the funds. The prospectuses of these funds explain the circumstances under which the funds will use fair value pricing and the effects of using fair value pricing.

Policies to Prevent Market Timing . Frequent purchases and redemptions of Fund shares may present risks for other shareholders of the Fund, which may include, among other things, interference in the efficient management of the Fund’s portfolio, dilution in the value of Fund shares held by long-term shareholders, increased brokerage and administrative costs and forcing the Fund to hold excess levels of cash.

The Fund is intended as a long-term investment. Therefore, the Trust’s Board of Trustees has adopted policies and procedures designed to detect and prevent inappropriate short-term trading activity that is harmful to the Fund. Because most of the interests in the Fund are held by investors indirectly through one or more financial intermediaries, the Fund does not generally have information about the identity of those investors or about transactions effected by those investors. Rather, the Fund and its service providers periodically review cash inflows and outflows from and to those intermediaries in an attempt to detect inappropriate trading activity by investors holding shares through those intermediaries. The Fund may not be able to determine whether trading by an investor holding shares through a financial intermediary is engaged in trading activity in the Fund’s shares that may be harmful to the Fund or its shareholders.

The Fund reserves the right in its discretion to reject any purchase, in whole or in part including, without limitation, by a person whose trading activity in Fund shares the Adviser believes could be harmful to the Fund. The Fund may decide to restrict purchase activity in its shares based on various factors, including, without limitation, whether frequent purchase and sale activity will disrupt portfolio management strategies and adversely affect performance. There can be no assurance that the Fund, the Adviser or State Street will identify all frequent purchase and sale activity affecting the Fund.

Distribution/Servicing (Rule 12b-1) Plan

The Fund has adopted a distribution plan under which the Fund may compensate its distributor (or others) for services in connection with the distribution of the Fund’s shares and for services provided to Fund shareholders. The plan calls for payments at an annual rate (based on average daily net assets) of 0.25%. Because these fees are paid out of the Fund’s assets on an ongoing basis, they will increase the cost of your investment and may cost you more over time than paying other types of sales charges.

Additional Payments to Financial Intermediaries

Dividends, Distributions and Tax Considerations

Income dividends and capital gains distributions of the Fund will be declared and paid at least annually.

The Fund intends to elect to be treated and qualify each year as a regulated investment company. A regulated investment company is generally not subject to tax at the corporate level on income and gains that are distributed to shareholders. However, the Fund’s failure to qualify as a regulated investment company would result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

For federal income tax purposes, distributions of investment income are generally taxable to you as ordinary income. Taxes on distributions of capital gains generally are determined by how long the Portfolio owned the investments that generated them, rather than how long you have owned your Fund shares. Distributions of net capital gains (that is, the excess of net long-term capital gains over net short-term capital losses) from the sale of investments that the Portfolio owned for more than one year that are properly designated by the Fund as capital gains dividends generally will be taxable to you as long-term capital gains. For individual taxpayers long-term capital gain rates have been temporarily reduced--in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets--for taxable years beginning before January 1, 2011. Distributions of gains from investments that the Portfolio owned for one year or less generally will be taxable to you as ordinary income. For the taxable years beginning before January 1, 2011, distributions of investment income designated by the Fund as derived from “qualified dividend income” are taxed at the rates applicable to long-term capital gain, provided holding period and other requirements are met by both the shareholder and the Fund level.

Distributions are taxable to you even if they are paid from income or gains earned by the Fund before your investment (and thus were included in the price you paid for your shares). Distributions may also be subject to state and local taxes and are taxable whether you receive them in cash or reinvest them in additional shares.

Financial Highlights

The Financial Highlights table is not presented because the Fund had not commenced operations as of the date of this Prospectus.

For more information about STATE STREET EQUITY 2000 INDEX FUND:

The Fund’s statement of additional information (SAI) includes additional information about the Fund and is incorporated by reference into this document. Additional information about the Fund’s investments will be available in the Fund’s annual and semi-annual reports to shareholders. In the Fund’s annual report, you will find a discussion of the market conditions and investment strategies that significantly affected the Fund’s performance during its last fiscal year.

SSgA FUNDS MANAGEMENT, INC.

State Street Financial Center

One Lincoln Street

Boston, Massachusetts 02111

The State Street Institutional Investment Trust’s Investment Company Act File Number is 811-09819.

STATE STREET INSTITUTIONAL INVESTMENT TRUST

_______________

STATE STREET AGGREGATE

BOND INDEX FUND

_______________

PROSPECTUS DATED APRIL __, 2010

_______________

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

AN INVESTMENT IN THE STATE STREET AGGREGATE BOND INDEX FUND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY.

Fund Summary
Other Investment Considerations And Risks
Management and Organization
Shareholder Information
Portfolio Holdings Disclosure
Distribution Servicing Plan and Payments to Financial Intermediaries
Dividends, Distributions and Tax Considerations
Financial Highlights

Fund Summary

Investment Objective

The Fund’s investment objective is to replicate as closely as possible, before expenses, the performance of the Barclays Capital U.S. Aggregate Index (the “U.S. Aggregate Index”). The Fund seeks to achieve its investment objective by investing substantially all of its investable assets in the State Street Aggregate Bond Index Portfolio (the “Aggregate Bond Index Portfolio” or sometimes referred to in context as the “Portfolio”) of the State Street Master Funds that has the same investment objective as, and investment policies that are substantially similar to those of, the Fund. In reviewing the investment policies of the Fund below, you should assume that the investment policies of the Portfolio are the same in all material respects as those of the Fund. There is no assurance that the Fund will achieve its investment objective.

Fees and Expenses of the Fund

The table describes the estimated fees and expenses that you may pay if you buy and hold shares of the Fund. As a shareholder in a Portfolio, the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time continues to pay its own fees and expenses. The table and the Example reflect the expenses of both the Fund and the Portfolio.

Shareholder Fees

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees	0.10%
Distribution (12b-1) Fees	0.25%
Other Expenses (2)	___ %
Total Annual Fund Operating Expenses	___ %

____________

(1)	Amounts reflect the total estimated expenses of the Portfolio and the Fund.

(2)	Other Expenses are based on estimated amounts for the current fiscal year.

Example

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

1 YEAR	3 YEARS
$___	$___

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). As a shareholder of the Portfolio the Fund bears its ratable share of the transaction costs associated with the portfolio turnover of the Portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. The Fund’s portfolio turnover rate has been omitted because the Fund had not commenced investment operations as of the date of this Prospectus.

Principal Investment Strategies

The Portfolio uses a management strategy designed to track the performance of the U.S. Aggregate Index. The U.S. Aggregate Index is a well-known fixed-income securities index, that represents investment grade debt securities and includes U.S. government securities, mortgage-backed securities and corporate debt securities.

The Adviser seeks to track the performance of the U.S. Aggregate Index by investing in debt securities and other investments that are representative of the U.S. Aggregate Index as a whole. Due to the large number of securities in the U.S. Aggregate Index and the fact that certain Index securities are unavailable for purchase, complete replication is not possible. Rather, the Portfolio intends to select securities that the Adviser believes will track the U.S. Aggregate Index in terms of industry weightings, market capitalization and other characteristics. Under normal market conditions, the Portfolio will not invest less than 80% of its total assets in securities in the Index. Shareholders will receive 60 days’ notice prior to a change in the 80% investment policy.

The Portfolio may make direct investments in U.S. government securities; corporate debt securities; mortgage-backed and other asset-backed securities; commercial paper, notes, and bonds issued by domestic and foreign corporations; and instruments of U.S. and foreign banks, including certificates of deposit, time deposits, letters of credit, and bankers’ acceptances. Securities in which the Portfolio invests may be fixed-income securities, zero-coupon securities, or variable rate securities.

In addition, the Portfolio may at times purchase or sell futures contracts on fixed-income securities, or options on those futures, in lieu of investing directly in fixed-income securities themselves. The Portfolio may also purchase or sell futures contracts and options on the U.S. Aggregate Index (or other fixed-income securities indices), if and when they become available. The Portfolio might do so, for example, in order to adjust the interest-rate sensitivity of the Portfolio to bring it more closely in line with that of the Index. It might also do so to increase its investment exposure pending investment of cash in the bonds comprising the Index or to reduce its investment exposure in situations where it intends to sell a portion of the securities in its portfolio but the sale has not yet been completed. The Portfolio may also enter into other derivatives transactions, including the use of options or swap transactions, to assist in attempting to replicate the performance of the Index. The Portfolio may also, to the extent permitted by applicable law, invest in shares of other mutual funds whose investment objectives and policies are similar to those of the Portfolio.

Principal Risks

Values of fixed-income securities could decline generally in response to changes in interest rates or other factors. In general, the price of a fixed-income security will fall when interest rates rise and will rise when interest rates fall. Securities with longer maturities may be more sensitive to interest rate changes than securities with shorter maturities.

Returns on investments in fixed-income securities could trail the returns on other investment options, including investments in equity securities.

Issuers of the Portfolio’s investments may not make timely payments of interest and principal or may fail to make such payments at all.

The Portfolio’s return may not match the return of the Index for a number of reasons. For example, the return on the securities and other investments selected by the Adviser may not correlate precisely with the return on the Index. The Portfolio incurs a number of operating expenses not applicable to the Index, and incurs costs in buying and selling securities. The Portfolio may not be fully invested at times, either as a result of cash flows into the Portfolio or reserves of cash held by the Portfolio to meet redemptions. The return on the sample of securities purchased by the Portfolio, or futures or other derivative positions taken by the Portfolio, to replicate the performance of the Index may not correlate precisely with the return of the Index.

Master/Feeder Structure Risk . Unlike a traditional mutual fund that invests directly in securities, the Fund pursues its objective by investing substantially all of its assets in the Master Portfolio with substantially the same investment objectives, policies and restrictions. The ability of the Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of the Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the corresponding Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio. The Adviser also serves as investment adviser to the Portfolio. Therefore, conflicts may arise as the Adviser fulfills its fiduciary responsibilities to the Fund and its corresponding Portfolio. For example, the Adviser may have an economic incentive to maintain the Fund’s investment in the Portfolio at a time when it might otherwise choose not to do so.

Performance

Performance information for the Fund has been omitted because the Fund had not commenced investment operations as of the date of this Prospectus.

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account	$25,000,000
To add to an existing account	No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

BY MAIL:

State Street Aggregate Bond Index Fund

P.O. Box 5493

Boston, MA 02206

BY OVERNIGHT:

State Street Aggregate Bond Index Fund

200 Clarendon Street

Boston, MA 02116

BY TELEPHONE:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

Other Investment Considerations and Risks

The U.S. Aggregate Index . The U.S. Aggregate Index is a well-known bond market index that covers the U.S. investment-grade fixed-income bond market, including government, corporate, mortgage-backed and asset-backed bonds, all with maturities of over one year. Bonds in the Index are weighted according to their market capitalizations. The composition of the Index is determined by Barclays Capital and is based on such factors as the market capitalization of each bond, its remaining time to maturity and quality rating as determined by Moody’s Investor Securities, Inc., an outside rating agency, and may be changed from time to time. The Fund and Portfolio are not sponsored, endorsed, sold, or promoted by Barclays Capital, and Barclays Capital makes no representation regarding the advisability of investing in the Fund or Portfolio.

Debt Securities . The values of debt securities generally rise and fall inversely with changes in interest rates. Interest rate risk is usually greater for debt securities with longer maturities. The Portfolio’s investments will normally include debt securities with longer maturities, although the Adviser will seek to ensure that the maturity characteristics of the Portfolio as a whole will generally be similar to those of the U.S. Aggregate Index. Mortgage-backed and asset-backed securities are also subject to increased interest rate risk, because prepayment rates on such securities typically increase as interest rates decline and decrease as interest rates rise. Changes in prepayment rates on mortgage-backed and asset-backed securities effectively increase and decrease the Portfolio’s average maturity when that is least desirable. The Portfolio will also be subject to credit risk (the risk that the issuer of a security will fail to make timely payments of interest and principal).

Futures Contracts and Related Options . The Portfolio may buy and sell futures contracts on securities contained in the U.S. Aggregate Index and options on those futures contracts. A “futures contract” on debt securities (such as U.S. Treasury securities) is a contract to buy or sell the securities at an agreed price on a specified future date. Depending on the change in value of the futures contract between the time when the Portfolio enters into and closes out a future or option transaction, the Portfolio realizes a gain or loss. Options and futures transactions involve risks. For example, it is possible that changes in the prices of futures contracts will not correlate precisely with changes in the value of the underlying security. In those cases, use of futures contracts and related options might decrease the correlation between the return of the Portfolio and the return of the Index. In addition, the Portfolio incurs transaction costs in entering into, and closing out, positions in futures contracts and related options. These costs typically have the effect of reducing the correlation between the return of the Portfolio and the return of the Index. Because the secondary market for futures contracts and options may be illiquid, the Portfolio may have to hold a contract or option when the Adviser would otherwise have sold it, or it may only be able to sell at a price lower than what the Adviser believes is the fair value of the contract or option, thereby potentially reducing the return of the Portfolio.

Other Derivative Transactions . The Portfolio may enter into derivatives transactions involving options and swaps. These transactions involve many of the same risks as those described above under “Futures Contracts and Related Options.” In addition, since many of such transactions are conducted directly with counterparties, and not on an exchange or board of trade, the Portfolio’s ability to realize any investment return on such transactions may depend on the counterparty’s ability or willingness to meet its obligations.

Securities Lending . The Portfolio may lend portfolio securities with a value of up to 33-1/3% of its total assets. For these purposes, total assets shall include the value of all assets received as collateral for the loan. Such loans may be terminated at any time, and the Portfolio will receive cash or other obligations as collateral. In a loan transaction, as compensation for lending its securities, the Portfolio will receive a portion of the dividends or interest accrued on the securities held as collateral or, in the case of cash collateral, a portion of the income from the investment of such cash. In addition, the Portfolio will receive the amount of all dividends, interest and other distributions on the loaned securities. However, the borrower has the right to vote the loaned securities. The Portfolio will call loans to vote proxies if a material issue affecting the investment is to be voted upon. Should the borrower of the securities fail financially, the Portfolio may experience delays in recovering the securities or exercising its rights in the collateral. Loans are made only to borrowers that are deemed by the securities lending agent to be of good financial standing. In a loan transaction, the Portfolio will also bear the risk of any decline in value of securities acquired with cash collateral. The Portfolio will minimize this risk by limiting the investment of cash collateral to high quality instruments of short maturity. This strategy is not used to leverage the Portfolio.

Portfolio Holdings Disclosure

The Fund’s portfolio holdings disclosure policy is described in the Statement of Additional Information.

Management and Organization

The Fund and the Portfolio . The State Street Aggregate Bond Index Fund (the “Fund”) is a mutual fund that seeks to provide an investment return matching, as closely as possible before expenses, the performance of the Barclays Capital U.S. Aggregate Index (the “U.S. Aggregate Index”). The Fund is a separate, diversified series of the State Street Institutional Investment Trust (the “Trust”), which is an open-end management investment company organized as a business trust under the laws of the Commonwealth of Massachusetts.

The Adviser . State Street Global Advisors “SSgA” is the investment management group of State Street Corporation, a publicly held bank holding company, and includes the Adviser, SSgA FM a wholly-owned subsidiary. SSgA is one of the world’s largest institutional money managers, and uses quantitative and traditional techniques to manage approximately $1.91 trillion as of December 31, 2009 in investment programs and portfolios for institutional and individual investors. SSgA FM, as the investment adviser to the Fund and the Portfolio, is registered with the Securities and Exchange Commission (“SEC”) under the Investment Advisers Act of 1940, as amended. SSgA FM had approximately $168.4 billion in assets under management at December 31, 2009. The Fund has entered into an investment advisory agreement with the Adviser, pursuant to which the Adviser will manage the Fund’s assets directly, for compensation paid at an annual rate of 0.10% of the Fund’s average daily net assets, in the event that the Fund were to cease investing substantially all of its assets in the Portfolio. The Adviser does not receive any fees from the Fund under that agreement so long as the Fund continues to invest substantially all of its assets in the Portfolio or in another investment company. The Adviser places all orders for purchases and sales of the Portfolio’s investments.

The Adviser’s principal address is State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111.

The Distributor . State Street Global Markets, LLC serves as the Fund’s distributor (the “Distributor”) pursuant to the Distribution Agreement between the Distributor and the Trust.

Shareholder Information

Determination of Net Asset Value. The Fund determines its net asset value (“NAV”) per share each business day as of the close of regular trading on the New York Stock Exchange (“NYSE”). The NAV per share is based on the market value of the securities held in the Fund. The NAV per share is calculated by dividing the value of the assets less liabilities of the Fund by the number of shares outstanding. The Fund values each security pursuant to guidelines adopted by the Board of Trustees. Securities may be valued at fair value, as determined in good faith and pursuant to procedures approved by the Portfolio’s Board of Trustees, under certain limited circumstances. For example, fair value pricing may be used when market quotations are not readily available or reliable, such as when (i) trading for a security is restricted; or (ii) a significant event, as determined by the Adviser, that may affect the value of one or more securities held by the Fund occurs after the close of a related exchange but before the determination of the Fund’s NAV. Attempts to determine the fair value of securities introduce an element of subjectivity to the pricing of securities. As a result, the price of a security determined through fair valuation techniques may differ from the price quoted or published by other sources and may not accurately reflect the price the Fund would have received had it sold the investment.

Policies to Prevent Market Timing . Frequent purchases and redemptions of Fund shares may present risks for other shareholders of the Fund, which may include, among other things, interference in the efficient management of the Fund’s portfolio, dilution in the value of Fund shares held by long-term shareholders, increased brokerage and administrative costs and forcing the Fund to hold excess levels of cash.

The Fund is intended as a long-term investment. Therefore, the Trust’s Board of Trustees has adopted policies and procedures designed to detect and prevent inappropriate short-term trading activity that is harmful to the Fund. Because most of the interests in the Fund are held by investors indirectly through one or more financial intermediaries, the Fund does not generally have information about the identity of those investors or about transactions effected by those investors. Rather, the Fund and its service providers periodically review cash inflows and outflows from and to those intermediaries in an attempt to detect inappropriate trading activity by investors holding shares through those intermediaries. The Fund may not be able to determine whether trading by an investor holding shares through a financial intermediary is engaged in trading activity in the Fund’s shares that may be harmful to the Fund or its shareholders.

The Fund reserves the right in its discretion to reject any purchase, in whole or in part including, without limitation, by a person whose trading activity in Fund shares the Adviser believes could be harmful to the Fund. The Fund may decide to restrict purchase activity in its shares based on various factors, including, without limitation, whether frequent purchase and sale activity will disrupt portfolio management strategies and adversely affect performance. There can be no assurance that the Fund, the Adviser or State Street will identify all frequent purchase and sale activity affecting the Fund.

Distribution/Servicing (Rule 12b-1) Plan

The Fund has adopted a distribution plan under which the Fund may compensate its distributor (or others) for services in connection with the distribution of the Fund’s shares and for services provided to Fund shareholders. The plan calls for payments at an annual rate (based on average daily net assets) of 0.25%. Because these fees are paid out of the Fund’s assets on an ongoing basis, they will increase the cost of your investment and may cost you more over time than paying other types of sales charges.

Additional Payments to Financial Intermediaries

Dividends, Distributions and Tax Considerations

Income dividends and capital gains distributions of the Fund will be declared and paid at least annually.

The Fund intends to elect to be treated and qualify each year as a regulated investment company. A regulated investment company is generally not subject to tax at the corporate level on income and gains that are distributed to shareholders. However, the Fund’s failure to qualify as a regulated investment company would result in corporate level taxation, and consequently, a reduction in income available for distribution to shareholders.

For federal income tax purposes, distributions of investment income are generally taxable to you as ordinary income. Taxes on distributions of capital gains generally are determined by how long the Portfolio owned the investments that generated them, rather than how long you have owned your Fund shares. Distributions of net capital gains (that is, the excess of net long-term capital gains over net short-term capital losses) from investments that the Portfolio owned for more than one year that are properly designated by the Fund as capital gain dividends generally will be taxable to you as long-term capital gains. Generally, the Fund does not expect a significant portion of its distributions to be capital gain dividends. For individual taxpayers long-term capital gain rates have been temporarily reduced--in general, to 15% with lower rates applying to taxpayers in the 10% and 15% rate brackets--for taxable years beginning before January 1, 2011. Distributions of gains from investments that the Portfolio owned for one year or less generally will be taxable to you as ordinary income. For taxable years beginning before January 1, 2011, distributions of investment income designated by the Fund as derived from “qualified dividend income” are taxed at the rates applicable to long-term capital gain provided holding period and other requirements are met by both the shareholder and the Fund; however, the Fund does not expect a significant portion of Fund distributions to be derived from qualified dividend income.

Distributions are taxable to you even if they are paid from income or gains earned by the Fund before your investment (and thus were included in the price you paid for your shares.) Distributions may also be subject to state and local taxes and are taxable whether you receive them in cash or reinvest them in additional shares.

Financial Highlights

The Financial Highlights table is not presented because the Fund had not commenced operations as of the date of this Prospectus.

For more information about STATE STREET AGGREGATE BOND INDEX FUND:

The Fund’s statement of additional information (SAI) includes additional information about the Fund and is incorporated by reference into this document. Additional information about the Fund’s investments will be available in the Fund’s annual and semi-annual reports to shareholders. In the Fund’s annual report, you will find a discussion of the market conditions and investment strategies that significantly affected the Fund’s performance during its last fiscal year.

SSGA FUNDS MANAGEMENT, INC .

State Street Financial Center

One Lincoln Street

Boston, Massachusetts 02111

The State Street Institutional Investment Trust’s Investment Company Act File Number is 811-09819.

STATE STREET INSTITUTIONAL INVESTMENT TRUST

STATE STREET INSTITUTIONAL LIMITED DURATION BOND FUND

Prospectus Dated April __, 2010

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

AN INVESTMENT IN THE STATE STREET INSTITUTIONAL LIMITED DURATION BOND FUND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY.

Fund Summary	3
Additional Information About the Fund’s and Portfolio’s Investment Strategies and Risks	8
Management and Organization	11
Shareholder Information	12
Portfolio Holdings Disclosure	11
Distribution Servicing Plan and Payments to Financial Intermediaries	15
Dividends, Distributions and Tax Considerations	15
Financial Highlights	17

Fund Summary

Investment Objective

The Fund seeks to achieve its investment objective by investing substantially all of its investable assets in the State Street Limited Duration Bond Portfolio (the “Limited Duration Bond Portfolio” or sometimes referred to in context as the “Portfolio”) of State Street Master Funds, which has the same investment objective as, and investment policies that are substantially similar to those of, the Fund. The Adviser is the investment adviser to the Portfolio. There is no assurance that the Fund will achieve its investment objective.

Fees and Expenses of the Fund

The table describes the estimated fees and expenses that you may pay if you buy and hold shares of the Fund. As a shareholder in the Portfolio, the Fund bears its ratable share of the Portfolio’s expenses, including advisory and administrative fees, and at the same time pays its own fees and expenses. The table and the Example reflect the estimated expenses of both the Fund and the Portfolio.

Shareholder Fees

(expenses that you pay each year as a percentage of the value of your investment) (1)

Management Fees		0.10	%
Distribution (12b-1) Fees		0.05	%
Other Expenses (2)	____		%
Total Annual Fund Operating Expenses	____		%

(1)

Amounts reflect total estimated expenses of the Portfolio and the Fund.

(2)

Other Expenses are estimated for the current fiscal year.

Example

This Example is intended to help you compare the cost of investing in the Fund with the costs of investing in other mutual funds.

1 year				3 years
$	___			$	___

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. The Fund’s portfolio turnover rate has been omitted because the Fund had not commenced investment operations as of the date of this Prospectus.

Principal Investment Strategies

The Fund invests in a Portfolio, which attempts to meet its objective by investing at least 65% of its assets in a diversified portfolio of dollar-denominated debt securities (those of medium and high quality) and maintains a dollar-weighted average portfolio duration of two years or less. These securities include mortgage related securities, corporate notes, variable and floating rate notes and asset-backed securities. The Portfolio may also invest in derivative instruments, such as futures contracts, options, interest rate swaps, default/credit swaps, total return swaps and other structured investments, as a substitute for investments directly in securities, to adjust the sensitivity of the Portfolio’s portfolio of investments to changes in interest rates, or otherwise to increase the Portfolio’s investment return. The Adviser will actively trade the Portfolio’s portfolio securities in an attempt to benefit from short-term yield disparities among different issues of fixed-income securities, or otherwise to increase the Portfolio’s investment return.

Principal Risks

Asset-Backed Securities Risk . Asset-backed securities are obligations whose principal and interest payments are supported or collateralized by pools of other assets, such as automobile loans, credit card receivables or leases. Defaults on the underlying assets may impair the value of an asset-backed security. There may be legal and practical limitations on the enforceability of any security interest granted with respect to those underlying assets. Asset-backed securities are also subject to prepayment risk, described below.

Credit/Default Risk . Credit risk is the risk that an issuer, guarantor or liquidity provider of a fixed-income security held by a fund may default on its obligation to pay scheduled interest and repay principal. It includes the risk that one or more of the securities will be downgraded by a credit rating agency; generally, lower rated issuers have higher credit risks. Credit risk also includes the risk that an issuer or guarantor of a security, or a bank or other financial institution that has entered into a repurchase agreement with the fund, may default on its payment or repurchase obligation, as the case may be. Credit risk generally is inversely related to credit quality.

Extension Risk . Extension risk is the risk that an issuer will exercise its right to repay principal on an obligation held by a Portfolio later than expected. This may happen when there is a rise in interest rates. Under these circumstances, the value of the obligation will decrease, thus preventing the Portfolio from investing expected repayment proceeds in securities paying yields higher than the yields paid by the securities that were expected to be repaid.

Foreign Investment Risk . The Portfolio may invest in U.S. dollar-denominated obligations issued by non-U.S. issuers. While such instruments may be denominated in U.S. dollars, this does not eliminate the risk inherent in investing in the securities of foreign issuers. Dollar-denominated instruments issued by entities located in foreign countries could lose value as a result of political, financial and economic events in foreign countries. Issuers of these instruments are not necessarily subject to the same regulatory requirements that apply to U.S. banks and corporations, although the information available for dollar-denominated instruments may be subject to the accounting, auditing and financial reporting standards of the U.S. domestic market or exchange on which they are traded, which standards may be more uniform and more exacting than those to which many foreign issuers are subject. Furthermore, by investing in dollar-denominated instruments rather than directly in a foreign issuer’s stock, the Portfolio can avoid currency risks during the settlement period for either purchases or sales .

Interest Rate Risk . During periods of rising interest rates, the Portfolio’s yield generally is lower than prevailing market rates causing the value of the Portfolio to fall. In periods of falling interest rates, the Portfolio’s yield generally is higher than prevailing market rates, causing the value of the Portfolio to rise. Typically, the more distant the expected cash flow that the Portfolio is to receive from a security, the more sensitive the market price of the security is to movements in interest rates. If a Portfolio owns securities that have variable or floating interest rates, as interest rates fall, the income the Portfolio receives from those securities also will fall.

Master/Feeder Structure Risk . Unlike a traditional mutual fund that invests directly in securities, the Fund pursues its objective by investing substantially all of its assets in the Master Portfolio which has substantially the same investment objectives, policies and restrictions. The ability of the Fund to meet its investment objective is directly related to the ability of the Portfolio to meet its objective. The ability of the Fund to meet its objective may be adversely affected by the purchase and redemption activities of other investors in the corresponding Portfolio. The ability of the Fund to meet redemption requests depends on its ability to redeem its interest in the Portfolio. The Adviser also serves as investment adviser to the Portfolio. Therefore, conflicts may arise as the Adviser fulfills its fiduciary responsibilities to the Fund and its corresponding Portfolio. For example, the Adviser may have an economic incentive to maintain the Fund’s investment in the Portfolio at a time when it might otherwise choose not to do so.

Mortgage-Backed Securities Risk . Mortgage-backed securities represent a participation in, or an investment in a pool secured by, mortgage loans. Each mortgage pool underlying mortgage-backed securities consists of mortgage loans. Traditional debt instruments typically pay a fixed rate of interest until maturity, when the entire principal amount is due. By contrast, payments on mortgage-backed and many asset-backed instruments typically include both interest and partial payment of principal. These securities may have less potential for capital appreciation and prepayment rates on mortgage-backed securities may reduce the Portfolio’s yield.

Prepayment Risk . Prepayment risk and extension risk apply primarily to asset-backed and mortgage-backed securities and certain municipal securities.

Sector Risk . The risk that the Portfolio concentrates its investment in specific industry sectors that have historically experienced substantial price volatility. The Portfolio is subject to greater risk of loss as a result of adverse economic, business or other developments than if its investments were diversified across different industry sectors. Securities of issuers held by the Portfolio may lack sufficient market liquidity to enable the Portfolio to sell the securities at an advantageous time or without a substantial drop in price.

U.S. Government Sponsored Enterprises Risk . Securities issued or guaranteed by certain agencies and instrumentalities of the U.S. government are not guaranteed or supported by the full faith and credit of the United States.

Performance

Performance information for the Fund has been omitted because the Fund had not commenced investment operations as of the date of this Prospectus.

Investment Adviser

SSgA Funds Management, Inc. serves as the investment adviser to the Fund.

Purchase and Sale of Fund Shares

Purchase Minimums

To establish an account		$	5,000,000
To add to an existing account		No minimum

Written Requests and Wire Transfers . You may redeem Fund shares by written request or wire transfer. Written requests should be sent to:

BY MAIL:

State Street Limited Duration Bond Fund

P.O. Box 8048

Boston, MA 02266-8048

BY OVERNIGHT:

State Street Institutional Limited Duration Bond Fund

30 Dan Road

Canton, MA 02021-2809

BY TELEPHONE:

Tax Information

Payments to Brokers, Banks and Other Financial Intermediaries

Additional Information About the Fund’s and Portfolio’s Investment Strategies and Risks

The investment strategies and risks below reflect the Fund’s and Portfolio’s current practices. This information supplements the principal investment strategies and risks explained above.

Asset-Backed Securities . Asset-backed securities are securities whose principal and interest payments are collateralized by pools of assets such as auto loans, credit card receivables, leases, installment contracts and personal property. Payments of principal and interest are passed through to holders of the securities and are typically supported by some form of credit enhancement, such as over collateralization, a letter of credit, surety bond, limited guarantee by another entity or by priority to certain of the borrower’s other securities. The degree of credit enhancement varies, generally applying only until exhausted and covering only a fraction of the security’s par value. If the credit enhancement of an asset-backed security held by the Portfolio has been exhausted, and if any required payments of principal and interest are not made with respect to the underlying loans, the Portfolio may experience loss or delay in receiving payment and a decrease in the value of the security.

Like mortgage-backed securities, asset-backed securities are often subject to more rapid repayment than their stated maturity date would indicate as a result of the pass-through of prepayments of principal on the underlying loans. During periods of declining interest rates, prepayment of loans underlying asset-backed securities can be expected to accelerate. The Portfolio’s ability to maintain positions in such securities will be affected by reductions in the principal amount of such securities resulting from prepayments, and its ability to reinvest the returns of principal at comparable yields is subject to generally prevailing interest rates at that time. To the extent that the Portfolio invests in asset-backed securities, the values of the Portfolio’s portfolio securities will vary with changes in market interest rates generally and the differentials in yields among various kinds of asset-backed securities.

The Portfolio may gain investment exposure to mortgage-backed investments by entering into agreements with financial institutions to buy the investments at a fixed price at a future date. The Portfolio may or may not take delivery of the investments at the termination date of such an agreement, but will nonetheless be exposed to changes in value of the underlying investments during the term of the agreement.

Futures Contracts and Options on Futures . To invest cash for purposes of hedging the Portfolio’s other investments, the Portfolio may enter into futures contracts that relate to securities in which it may directly invest and indices comprised of such securities and may purchase and write call and put options on such contracts. The Portfolio may also purchase futures and options if cheaper than the underlying stocks or bonds.

A financial futures contract is a contract to buy or sell a specified quantity of financial instruments such as U.S. Treasury bills, notes and bonds, commercial paper and bank certificates of deposit or the cash value of a Financial instrument index at a specified future date at a price agreed upon when the contract is made. Under such contracts no delivery of the actual securities making up the index takes place. Rather, upon expiration of the contract, settlement is made by exchanging cash in an amount equal to the difference between the contract price and the closing price of the index at expiration, net at variation margin previously paid.

Substantially all futures contracts are closed out before settlement date or called for cash settlement. A futures contract is closed out by buying or selling an identical offsetting futures contract. Upon entering into a futures contract, the Portfolio is required to deposit an initial margin with a custodian for the benefit of the futures broker. The initial margin serves as a “good faith” deposit that the Portfolio will honor its futures commitments. Subsequent payments (called “variation margin”) to and from the broker are made on a daily basis as the price of the underlying investment fluctuates.

Options on futures contracts give the purchaser the right to assume a position at a specified price in a futures contract at any time before expiration of the option contract.

When trading futures contracts, the Portfolio will not commit more than 5% of the market value of its total assets to initial margin deposits on futures and premiums paid for options on futures. The Portfolio’s transactions, if any, in options, futures, options on futures and equity swaps involve additional risk of loss. Loss can result from a lack of correlation between changes in the value of derivative instruments and the portfolio assets (if any) being hedged, the potential illiquidity of the markets for derivative instruments, or the risks arising from margin requirements and related leverage factors associated with such transactions. The use of these management techniques also involves the risk of loss if the Adviser is incorrect in its expectation of fluctuations in securities prices, interest rates or currency prices. Please see Derivatives Risk in the Principal Risks section.

Government Securities . U.S. Government securities include U.S. Treasury bills, notes, and bonds and other obligations issued or guaranteed as to interest and principal by the U.S. Government or its agencies or instrumentalities. Obligations issued or guaranteed as to interest and principal by the U.S. Government, its agencies or instrumentalities include securities that are supported by the full faith and credit of the United States Treasury, securities that are supported by the right of the issuer to borrow from the United States Treasury, discretionary authority of the U.S. Government agency or instrumentality, and securities supported solely by the creditworthiness of the issuer.

Interest Rate Swaps, Default/Credit Swaps, Total Return Swaps, and Interest Rate Caps, Floors and Collars . Interest rate swaps involve the exchange by the Portfolio with another party of their respective commitments to pay or receive interest, such as an exchange of fixed-rate payments for floating rate payments. Default/credit swaps involve the receipt of floating or fixed-rate payments in exchange for assuming potential credit losses of an underlying security. Default/credit swaps give one party to a transaction the right to dispose of or acquire an asset (or group of assets), or the right to receive or make a payment from the other party, upon the occurrence of specified credit events. Total return swaps involve the receipt or payment of the “total return” of a defined underlying asset in exchange for the payment or receipt of a cash flow based on a predetermined floating rate. The purchase of an interest rate cap entitles the purchaser, to the extent that a specified index exceeds a predetermined interest rate, to receive payment of interest on a notional principal amount from the party selling such interest rate cap. The purchase of an interest rate floor entitles the purchaser, to the extent that a specified index falls below a predetermined interest rate, to receive payments of interest on a notional principal amount from the party selling the interest rate floor. An interest rate collar is the combination of a cap and a floor that preserves a certain return within a predetermined range of interest rates. The Portfolio may enter into swap transactions for hedging purposes or to seek to increase total return. The use of interest rate and default/credit swaps and total return swaps, as well as interest rate caps, floors and collars, is a highly specialized activity which involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. If the Adviser is incorrect in its forecasts of market values or interest rates, the investment performance of the Portfolio would be less favorable than it would have been if these investment techniques were not used. The Portfolio expects to enter into these transactions primarily to preserve a return or spread on a particular investment or portion of its portfolio or to protect against any increase in the price of securities it anticipates purchasing at a later date. These transactions are intended to be used as a hedge and not as a speculative investment. Please see Derivative Risk in the Principal Risks section.

Types of mortgage-related securities in which the Portfolio may invest include: Government National Mortgage Association (“GNMA”) Certificates (“Ginnie Maes”), Federal Home Loan Mortgage Corporation (“FHLMC”) Mortgage Participation Certificates (“Freddie Macs”), Federal National Mortgage Association (“FNMA”) Guaranteed Mortgage Certificates (“Fannie Maes”) and Commercial Mortgage-Backed Securities (“CMBS”). Mortgage certificates are mortgage-backed securities representing undivided fractional interests in pools of mortgage backed loans. These loans are made by mortgage bankers, commercial banks, savings and loan associations and other lenders. GNMA is authorized to guarantee the timely payment of the principal of an interest on certificates that are based on and backed by a pool of mortgage loans insured by the Federal Housing Administration (FHA Loans), or guaranteed by the Veterans Administration (VA Loans), or by pools of other eligible mortgage loans. In order to meet its obligations under any guaranty, GNMA is authorized to borrow from the United States Treasury in an unlimited amount. Each Fannie Mae is issued and guaranteed by FNMA and represents an undivided interest in a pool of mortgage loans formed by FNMA. The principal activity of FHLMC currently is the purchase of first lien, conventional, residential mortgage loans and participation interests in such mortgage loans and their resale in the form of mortgage securities, primarily Freddie Mac Certificates.

Traditional debt investments typically pay a fixed rate of interest until maturity, when the entire principal amount is due. By contrast, payments on mortgage-backed investments typically include both interest and partial payment of principal. Principal may also be prepaid voluntarily, or as a result of refinancing or foreclosure. The Portfolio may have to invest the proceeds from prepaid investments in other investments with less attractive terms and yields. As a result, these securities may have less potential for capital appreciation during periods of declining interest rates than other securities of comparable maturities, although they may have a similar risk of decline in market value during periods of rising interest rates. Because the prepayment rate generally declines as interest rates rise, an increase in interest rates will likely increase the duration, and thus the volatility, of mortgage-backed securities. In addition to interest rate risk, investments in mortgage-backed securities composed of subprime mortgages may be subject to a higher degree of credit risk, valuation risk and liquidity risk. Duration is a measure of the expected life of a fixed income security that is used to determine the sensitivity of the security's price to changes in interest rates. Unlike the maturity of a fixed income security, which measures only the time until final payment is due, duration takes into account the time until all payments of interest and principal on a security are expected to be made, including how these payments are affected by prepayments and by changes in interest rates.

Options on Securities . The Portfolio may write and purchase covered put and call options on securities in which it may directly invest. The total amount of premiums paid by the Portfolio for all put and call options held by it at any time will not exceed 5% of the value of the Portfolio’s total assets. Further, the Portfolio will not write a put or call option or combination thereof if, as a result, the aggregate value of all securities or collateral deliverable under its outstanding options would exceed 25% of the value of the Portfolio’s total assets.

Portfolio Duration . The Portfolio will maintain a dollar-weighted average portfolio duration of two years or less. Duration is a measure of the price sensitivity of a security to changes in interest rates. Unlike maturity, which measures the period of time until final payment is to be made on a security, duration measures the dollar-weighted average maturity of a security’s expected cash flows (i.e., interest and principal payments), discounted to their present values, after giving effect to all maturity shortening features, such as call or redemption rights. With respect to a variable or floating-rate instrument, duration is adjusted to indicate the price sensitivity of the instrument to changes in the interest rate in effect until the next reset date. For substantially all securities, the duration of a security is equal to or less than its stated maturity.

Repurchase Agreements . The Portfolio enters into repurchase agreements with banks and other financial institutions, such as broker-dealers. In substance, a repurchase agreement is a loan for which the Portfolio receives securities as collateral. Under a repurchase agreement, the Portfolio purchases securities from a financial institution that agrees to repurchase the securities at the Portfolio’s original purchase price plus interest within a specified time. Repurchase transactions are limited to those member banks of the Federal Reserve System and broker-dealers whose creditworthiness the Adviser considers satisfactory. If the other party or “seller” defaults, the Portfolio might suffer a loss to the extent that the proceeds from the sale of the underlying securities and other collateral held by the Portfolio are less than the repurchase price and the Portfolio’s cost associated with delay and enforcement of the repurchase agreement. In addition, in the event of a bankruptcy of the seller, the Portfolio may be delayed or prevented from recovering the collateral.

Section 4(2) Commercial Paper and Rule 144A Securities . The Portfolio may invest in commercial paper issued in reliance on the private placement exemption from registration afforded by Section 4(2) of the Securities Act of 1933, as amended (the “1933 Act”). This commercial paper is commonly called “Section 4(2) paper.” The Portfolio may also invest in securities that may be offered and sold only to “qualified institutional buyers” under Rule 144A of the 1933 Act (“Rule 144A securities”).

Section 4(2) paper is sold to institutional investors who must agree to purchase the paper for investment and not with a view to public distribution. Any resale by the purchaser must be in a transaction exempt from the registration requirements of the 1933 Act. Section 4(2) paper normally is resold to other institutional investors like the Portfolio through or with the assistance of the issuer or investment dealers that make a market in Section 4(2) paper. As a result it suffers from liquidity risk, the risk that the securities may be difficult to value because of the absence of an active market and the risk that it may be sold only after considerable expense and delay, if at all. Rule 144A securities generally must be sold only to other qualified institutional buyers.

Section 4(2) paper and Rule 144A securities will not be considered illiquid for purposes of the Portfolio’s limitation on illiquid securities if the Adviser (pursuant to guidelines adopted by the Board) determines that a liquid trading market exists for the securities in question. There can be no assurance that a liquid trading market will exist at any time for any particular Section 4(2) paper or Rule 144A securities. The Statement of Additional Information (“SAI”) addresses the Fund’s and Portfolio’s limitation on illiquid securities.

Variable and Floating Rate Securities . Variable and floating rate securities are instruments issued or guaranteed by entities such as: (1) the U.S. Government, or an agency or instrumentality thereof, (2) corporations, (3) financial institutions, (4) insurance companies, or (5) trusts. The Portfolio may purchase variable and floating rate securities issued or guaranteed by the U.S. government, or an agency or instrumentality thereof. A variable rate security provides for the automatic establishment of a new interest rate on set dates. Variable rate obligations whose interest is readjusted no less frequently than annually will be deemed to have a maturity equal to the period remaining until the next readjustment of the interest rate. A floating rate security provides for the automatic adjustment of its interest rate whenever a specified interest rate changes. Interest rates on these securities are ordinarily tied to, and are a percentage of, a widely recognized interest rate, such as the yield on 90-day U.S. Treasury bills or the prime rate of a specified bank. Generally, changes in interest rates will have a smaller effect on the market value of variable and floating rate securities than on the market value of comparable fixed-income obligations. Thus, investing in variable and floating rate securities generally allows less opportunity for capital appreciation and depreciation than investing in comparable fixed income securities. Securities purchased by a Portfolio may include variable and floating rate instruments, which may have a stated maturity in excess of the Portfolio’s maturity limitations but which will, except for certain U.S. government obligations, permit the Portfolio to demand payment of the principal of the instrument at least once every 13 months upon not more than 30 days’ notice. Variable and floating rate instruments may include variable amount master demand notes that permit the indebtedness thereunder to vary in addition to providing for periodic adjustments in the interest rate. There may be no active secondary market for a particular variable or floating rate instrument. Nevertheless, the periodic readjustments of their interest rates tend to assure that their value to the Portfolio will approximate their par value. Illiquid variable and floating rate instruments (instruments which are not payable upon seven days’ notice and do not have an active trading market) are subject to the Portfolio’s percentage limitations regarding securities that are illiquid or not readily marketable. The Adviser will continuously monitor the creditworthiness of issuers of variable and floating rate instruments in which the Portfolio invests, and their ability to repay principal and interest. Variable and floating rate securities are subject to interest rate and credit/default risk .

Temporary Defensive Strategies . At times, the Adviser may judge that market conditions make pursuing the Portfolio’s basic investment strategy inconsistent with the best interests of its shareholders. At such times, the Adviser may (but will not necessarily), without notice, temporarily use alternative strategies primarily designed to reduce fluctuations in the values of the Portfolio’s assets. In implementing these defensive strategies, the Portfolio may hold assets in cash and cash equivalents and in other investments that the Adviser believes to be consistent with the Portfolio’s best interests. Taking such a temporary defensive position may result in the Portfolio not achieving its investment objective.

Portfolio Holdings Disclosure

The Fund’s portfolio holdings disclosure policy is described in the Statement of Additional Information.

Management and Organization

The Fund and the Portfolio . The State Street Institutional Limited Duration Bond Fund (the “Fund”) is a mutual fund whose investment objective is to seek high current income and liquidity. The Fund is not a money market fund, and the Fund’s net asset value per share will fluctuate. The Fund is a separate, diversified series of the State Street Institutional Investment Trust (the “Trust”), which is an open-end management investment company organized as a business trust under the laws of the Commonwealth of Massachusetts.

The investment objective of the Fund as stated above is non-fundamental, which means that it may be changed without shareholder approval.

The Adviser . State Street Global Advisors (“SSgA”) is the investment management group of State Street Corporation, a publicly held bank holding company, and includes the Adviser, SSgA FM, a wholly-owned subsidiary. SSgA is one of the world’s largest institutional money managers, and uses quantitative and traditional techniques to manage approximately $1.91 trillion as of December 31, 2009 in investment programs and portfolios for institutional and individual investors. SSgA FM, as the investment adviser to the Fund and the Portfolio, is registered with the Securities and Exchange Commission (“SEC”) under the Investment Advisers Act of 1940, as amended (the “1940 Act”). SSgA FM had approximately $168.4 billion in assets under management at December 31, 2009. The Fund has entered into an investment advisory agreement with the Adviser pursuant to which the Adviser will manage the Fund’s assets directly, at an annual rate of .10% of the Fund’s average daily net assets, in the event that the Fund were to cease investing substantially all of its assets in the Portfolio. The Adviser does not receive any fees from the Fund under that agreement so long as the Fund continues to invest substantially all of its assets in the Portfolio or in another investment company. The Adviser places all orders for purchases and sales of the Portfolio’s investments.

The Adviser’s principal address is State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111.

The Administrator and Custodian . State Street Bank and Trust Company (“State Street”), a subsidiary of State Street Corporation, is the administrator and custodian.

The Transfer Agent and Dividend Disbursing Agent . Boston Financial Data Services, Inc. is the transfer agent and dividend disbursing agent.

The Distributor . State Street Global Markets, LLC serves as the Fund’s distributor (the “Distributor”) pursuant to the Distribution Agreement between the Distributor and the Trust.

Shareholder Information

Determination of Net Asset Value . The Fund determines the net asset value (“NAV”) per share once each business day as of the close of the regular trading session of the New York Stock Exchange (the “NYSE”). Pricing does not occur on NYSE holidays. A business day is one on which the NYSE is open for regular trading. The Federal Reserve is closed on certain holidays on which the NYSE is open. These holidays are Columbus Day and Veteran’s Day. On these holidays, you will not be able to purchase shares by wiring federal funds because federal funds wiring does not occur on days that the Federal Reserve is closed. The NAV per share for the Fund is computed by adding the value of all securities and other assets of the Fund, deducting accrued liabilities, dividing by the number of shares outstanding and rounding to the nearest cent.

Ordinarily, the Fund values each portfolio security based upon the last reported sales price or other market quotation for the security in the market in which the security principally trades. If market quotations are not readily available for a security or if subsequent events suggest that a market quotation is not reliable, the Fund will use the security’s fair value, as determined in accordance with procedures approved by the Board of Trustees. Because foreign securities sometimes trade on days when Fund shares are not priced, the value of the Fund’s portfolio may change on days when Fund shares cannot generally be purchased or redeemed. Debt obligation securities maturing within 60 days of the valuation date are valued at amortized cost.

Purchasing Shares . Investors pay no sales load to invest in the Fund. The price for Fund shares is the NAV per share. Purchase orders in good form and payment received the same day by Fed Wire will receive that day’s NAV and will earn dividends declared on the date of the purchase. All purchases that are made by check will begin earning dividends the following business day after the purchase date.

The minimum initial investment in the Fund is $5 million, although the Adviser may waive the minimum in its discretion. Holdings of all customer accounts of each Intermediary shall be aggregated for determining these account balances. There is no minimum subsequent investment, except in relation to maintaining certain minimum account balances (See “Redeeming Shares” below). The Fund intends to be as fully invested as is practicable; therefore, investments must be made in Federal Funds (i.e., monies credited to the account of the Fund’s custodian bank by a Federal Reserve Bank) received by the Fund before the order will be accepted. The Fund reserves the right to cease accepting investments at any time or to reject any investment order.

BY MAIL:

An initial investment in the Fund must be preceded or accompanied by a completed, signed Institutional Account Application Form, sent to:

State Street Institutional Limited Duration Bond Fund

P.O. Box 8048

Boston, MA 02266-8048

BY OVERNIGHT:

State Street Institutional Limited Duration Bond Fund

30 Dan Road

Canton, MA 02021-2809

BY TELEPHONE/FAX:

confirm receipt of the faxed Institutional Account Application Form (initial purchases only),

request your new account number (initial purchases only),

confirm the amount being wired and wiring bank, and

receive a confirmation number for your purchase order (your trade is not effective until you have received a confirmation number from the Fund),

For your initial investment, send the original, signed Institutional Account Application Form to the address above.

WIRE INSTRUCTIONS:

Instruct your bank to transfer money by Federal Funds wire to:

State Street Bank and Trust Company

2 Avenue de Lafayette

Boston, MA 02111

ABA# 011000028

DDA# 9905-801-8

State Street Institutional Limited Duration Bond Fund

Account Number

Account Registration

Redeeming Shares . An investor may withdraw all or any portion of its investment at the NAV next determined after it submits a withdrawal request, in proper form, to the Fund. Payments of redemption proceeds ordinarily will be sent the next business day. The Fund reserves the right to pay for redeemed shares within seven days after receiving your redemption order if, in the judgment of the Adviser, an earlier payment could adversely affect the Fund. The right of any investor to receive payment with respect to any withdrawal may be suspended or the payment of the withdrawal proceeds postponed during any period in which the NYSE is closed (other than weekends or holidays) or trading on the NYSE is restricted or, to the extent otherwise permitted by the 1940 Act, if an emergency exists.

If you are redeeming some, but not all, of your shares, your remaining account balance should be above $1,000,000 and subsequent purchases of shares of the Fund may be rejected unless, after such purchase, your account balance will be at or greater than $1,000,000. A request for a partial redemption by an investor whose account balance is below the minimum amount or a request for partial redemption by an investor that would bring the account below the minimum amount may be treated as a request for a complete redemption of the account. These minimums may be different for investments made through certain financial intermediaries as determined by their policies and may be waived in the Adviser’s discretion. The Fund reserves the right to modify or waive its minimum account requirements at any time with or without prior notice. The Fund also reserves the right to involuntarily redeem an investor’s account if the investor’s account balance falls below the applicable minimum amount due to transaction activity. Notification will be sent to the shareholder giving the shareholder 60 days to increase the account to the required minimum or the account may be closed.

BY MAIL