Supplement to the
Retirement Government Money Market Portfolio
October 30, 2015
Prospectus

The following information replaces similar information found in the "Fund Summary" section under the heading "Principal Investment Strategies" on page 4.

• Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments.

The following information supplements information found in the "Fund Summary" section under the heading "Principal Investment Strategies" on page 4.

In addition, the Adviser normally invests at least 80% of the fund's assets in U.S. Government securities and repurchase agreements for those securities.

The following information replaces the similar information found in the "Fund Summary" section under the heading "Principal Investment Risks" on page 4.

You could lose money by investing in the fund. Although the fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Fidelity Investments and its affiliates, the fund's sponsor, have no legal obligation to provide financial support to the fund, and you should not expect that the sponsor will provide financial support to the fund at any time.

The following information replaces the similar information found in the "Fund Basics" section under the heading "Principal Investment Strategies" on page 7.

In buying and selling securities for the fund, the Adviser complies with industry-standard regulatory requirements for money market funds regarding the quality, maturity, liquidity, and diversification of the fund's investments. The Adviser stresses maintaining a stable $1.00 share price, liquidity, and income.

In addition, the Adviser normally invests at least 80% of the fund's assets in U.S. Government securities and repurchase agreements for those securities.

The following information replaces similar information found in the "Fund Basics" section under the heading "Shareholder Notice" on page 8.

The following is subject to change only upon 60 days' prior notice to shareholders:

Retirement Government Money Market Portfolio normally invests at least 99.5% of its total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully and at least 80% of the fund's assets in U.S. Government securities and repurchase agreements for those securities.

RGM-16-02		April 14, 2016
1.478079.118

Supplement to the
Retirement Money Market Portfolio
October 30, 2015
Prospectus

Effective December 1, 2015, the fund has transitioned to a government money market fund and has changed its name to Retirement Government Money Market II Portfolio.

The following "Principal Investment Strategies" and "Principal Investment Risks" replace the existing information beginning on page 2.

Principal Investment Strategies

• Normally investing at least 99.5% of total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully (i.e., collateralized by cash or government securities).
• Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury.
• Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments.

In addition, the Adviser normally invests at least 80% of the fund's assets in U.S. Government securities and repurchase agreements for those securities.

Principal Investment Risks

• Interest Rate Changes. Interest rate increases can cause the price of a money market security to decrease.
• Issuer-Specific Changes. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a money market security to decrease.

You could lose money by investing in the fund. Although the fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Fidelity Investments and its affiliates, the fund's sponsor, have no legal obligation to provide financial support to the fund, and you should not expect that the sponsor will provide financial support to the fund at any time.

The fund will not impose a fee upon the sale of your shares, nor temporarily suspend your ability to sell shares if the fund's weekly liquid assets fall below 30% of its total assets because of market conditions or other factors.

The following "Principal Investment Strategies," "Description of Principal Security Types" and "Principal Investment Risks" replace the existing information beginning on page 7.

Principal Investment Strategies

The Adviser normally invests at least 99.5% of the fund's total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully (i.e., collateralized by cash or government securities). Certain issuers of U.S. Government securities are sponsored or chartered by Congress, but their securities are neither issued nor guaranteed by the U.S. Treasury.

In buying and selling securities for the fund, the Adviser complies with industry-standard regulatory requirements for money market funds regarding the quality, maturity, liquidity, and diversification of the fund's investments. The Adviser stresses maintaining a stable $1.00 share price, liquidity, and income.

In addition, the Adviser normally invests at least 80% of the fund's assets in U.S. Government securities and repurchase agreements for those securities.

Description of Principal Security Types

Money market securities are high-quality, short-term securities that pay a fixed, variable, or floating interest rate. Securities are often specifically structured so that they are eligible investments for a money market fund. For example, in order to satisfy the maturity restrictions for a money market fund, some money market securities have demand or put features, which have the effect of shortening the security's maturity. Money market securities include bank certificates of deposit, bankers' acceptances, bank time deposits, notes, commercial paper, and U.S. Government securities.

U.S. Government securities are high-quality securities issued or guaranteed by the U.S. Treasury or by an agency or instrumentality of the U.S. Government. U.S. Government securities may be backed by the full faith and credit of the U.S. Treasury, the right to borrow from the U.S. Treasury, or the agency or instrumentality issuing or guaranteeing the security. Certain issuers of U.S. Government securities, including Fannie Mae, Freddie Mac, and the Federal Home Loan Banks, are sponsored or chartered by Congress but their securities are neither issued nor guaranteed by the U.S. Treasury.

A repurchase agreement is an agreement to buy a security at one price and a simultaneous agreement to sell it back at an agreed-upon price. A repurchase agreement entered into by the fund may be collateralized by U.S. Government securities or cash. A repurchase agreement is collateralized fully if the collateral consists entirely of U.S. Government securities and cash items.

Principal Investment Risks

Many factors affect the fund's performance. The fund's yield will change daily based on changes in interest rates and other market conditions. Although the fund is managed to maintain a stable $1.00 share price, there is no guarantee that the fund will be able to do so. For example, a major increase in interest rates or a decrease in the credit quality of the issuer of one of the fund's investments could cause the fund's share price to decrease.

The following factors can significantly affect the fund's performance:

Interest Rate Changes. Money market securities have varying levels of sensitivity to changes in interest rates. In general, the price of a money market security can fall when interest rates rise and can rise when interest rates fall. Securities with longer maturities and certain types of securities, such as the securities of issuers in the financial services sector, can be more sensitive to interest rate changes. Short-term securities tend to react to changes in short-term interest rates.

Issuer-Specific Changes. Changes in the financial condition of an issuer or counterparty, changes in specific economic or political conditions that affect a particular type of issuer, and changes in general economic or political conditions can increase the risk of default by an issuer or counterparty, which can affect a security's or instrument's credit quality or value. Entities providing credit support or a maturity-shortening structure also can be affected by these types of changes, and if the structure of a security fails to function as intended, the security could decline in value.

In response to market, economic, political, or other conditions, a fund may temporarily use a different investment strategy (including leaving a significant portion of the fund's assets uninvested) for defensive purposes. Uninvested assets do not earn income for a fund, which may have a significant negative impact on the fund's yield and may prevent the fund from achieving its investment objective.

The fund will not impose a fee upon the sale of your shares, nor temporarily suspend your ability to sell shares if the fund's weekly liquid assets fall below 30% of its total assets because of market conditions or other factors.

The following information supplements information found in the "Fund Basics" section above the "Valuing Shares" heading on page 8.

Shareholder Notice

The following is subject to change only upon 60 days' prior notice to shareholders:

Retirement Government Money Market II Portfolio normally invests at least 99.5% of its total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully and at least 80% of the fund's assets in U.S. Government securities and repurchase agreements for those securities.

RMM-16-02		April 14, 2016
1.478064.121

Supplement to the

Retirement Government Money Market Portfolio (FGMXX) and Retirement Money Market Portfolio (FRTXX)

Funds of Fidelity Money Market Trust

STATEMENT OF ADDITIONAL INFORMATION

October 30, 2015

Effective December 1, 2015, Retirement Money Market Portfolio has transitioned to a government money market fund and has changed its name to Retirement Government Money Market II Portfolio.

Effective December 1, 2015, the following information replaces similar information found in the "Investment Policies and Limitations" section beginning on page 3.

Concentration

For Retirement Government Money Market II Portfolio:

The fund may not purchase the securities of any issuer (other than securities issued or guaranteed by the U.S. Government or any of its agencies or instrumentalities) if, as a result, more than 25% of the fund's total assets would be invested in the securities of companies whose principal business activities are in the same industry.

For purposes of the fund's concentration limitation discussed above, with respect to any investment in repurchase agreements collateralized by U.S. Government securities, Fidelity Management & Research Company (FMR) looks through to the U.S. Government securities.

For purposes of the fund's concentration limitation discussed above, FMR may analyze the characteristics of a particular issuer and security and assign an industry or sector classification consistent with those characteristics in the event that the third-party classification provider used by FMR does not assign a classification.

The following information found in the "Investment Policies and Limitations" section on page 8 has been removed .

NRSROs. The Board of Trustees has designated each of the following nationally recognized statistical rating organizations (NRSROs) as a "designated NRSRO" pursuant to Rule 2a-7 under the 1940 Act: DBRS Ltd.; Fitch, Inc.; Moody's Investors Service, Inc.; and Standard & Poor's Ratings Services.

RMM-RGMB-16-01		April 14, 2016
1.475766.119