ALNYLAM PHARMACEUTICALS, INC. Restricted Stock Agreement

Exhibit 10.5

ALNYLAM PHARMACEUTICALS, INC.

Restricted Stock Agreement

Alnylam Pharmaceuticals, Inc. (the “Company”) has selected you to receive the restricted stock award described above, which is subject to the provisions of the Company’s 2009 Stock Incentive Plan (the “Plan”) and the terms and conditions contained in this Restricted Stock Agreement. Please confirm your acceptance of this restricted stock award and of the terms and conditions of this Agreement by signing a copy of this Agreement where indicated below.

ALNYLAM PHARMACEUTICALS, INC.

Restricted Stock Agreement

The terms and conditions of the award of shares of restricted common stock of the Company (the “Restricted Shares”) made to the Participant, as set forth on the cover page of this Agreement, are as follows:

1. Issuance of Restricted Shares.

(a) The Restricted Shares are issued to the Participant, effective as of the Grant Date (as set forth on the cover page of this Agreement), in consideration of employment services rendered and to be rendered by the Participant to the Company.

(b) The Restricted Shares will initially be issued by the Company in book entry form only, in the name of the Participant. Following the vesting of any Restricted Shares pursuant to Section 2 below, the Company shall, if requested by the Participant, issue and deliver to the Participant a certificate representing the vested Restricted Shares. The Participant agrees that the Restricted Shares shall be subject to the forfeiture provisions set forth in Section 3 of this Agreement and the restrictions on transfer set forth in Section 4 of this Agreement.

2. Vesting.

(a) Vesting Schedule. Unless otherwise provided in this Agreement or the Plan, the Restricted Shares shall vest in accordance with the following vesting schedule: [ ]% of the total number of Restricted Shares shall vest on the first anniversary of the Grant Date and [            ]% of the total number of Restricted Shares shall vest at the end of each successive [            ] period following the first anniversary of the Grant Date, through and including the [            ] anniversary of the Grant Date. Any fractional number of Restricted Shares resulting from the application of the foregoing percentages shall be rounded down to the nearest whole number of Restricted Shares.

(b) Acceleration of Vesting. Notwithstanding the foregoing vesting schedule, all unvested Restricted Shares shall vest effective (i) immediately prior to a Reorganization Event involving the liquidation or dissolution of the Company (as defined in the Plan), and (ii) immediately upon the Participant’s death if the Participant dies while in employment or service with the Company.

3. Forfeiture of Unvested Restricted Shares Upon Employment Termination.

In the event that the Participant ceases to be employed by, a director of, or a consultant or advisor to the Company for any reason or no reason, with or without cause, all of the Restricted Shares that are unvested as of the time of such termination from the Company, as well as any Accrued Dividends (as defined below) declared by the Company with respect to such unvested Restricted Shares, shall be forfeited immediately and automatically to the Company, without the payment of any consideration to the Participant, effective as of such termination of employment. The Participant hereby authorizes the Company to take any actions necessary or appropriate to

cancel any certificate(s) representing forfeited Restricted Shares and transfer ownership of such forfeited Restricted Shares to the Company; and if the Company or its transfer agent requires an executed stock power or similar confirmatory instrument in connection with such cancellation and transfer, the Participant shall promptly execute and deliver the same to the Company. The Participant shall have no further rights with respect to any Restricted Shares, or any Accrued Dividends with respect to such Restricted Shares, that are so forfeited. If the Participant is employed by a subsidiary of the Company, any references in this Agreement to employment with the Company shall instead be deemed to refer to employment with such subsidiary.

4. Restrictions on Transfer.

The Participant shall not sell, assign, transfer, pledge, hypothecate or otherwise dispose of, by operation of law or otherwise (collectively “transfer”) any Restricted Shares, or any interest therein, until such Restricted Shares have vested, except that the Participant may transfer such Restricted Shares: (a) to or for the benefit of any spouse, children, parents, uncles, aunts, siblings, grandchildren and any other relatives approved by the Compensation Committee (collectively, “Approved Relatives”) or to a trust established solely for the benefit of the Participant and/or Approved Relatives, provided that such Restricted Shares shall remain subject to this Agreement (including without limitation the forfeiture provisions set forth in Section 3 and the restrictions on transfer set forth in this Section 4) and such permitted transferee shall, as a condition to such transfer, deliver to the Company a written instrument confirming that such transferee shall be bound by all of the terms and conditions of this Agreement; or (b) as part of the sale of all or substantially all of the shares of capital stock of the Company (including pursuant to a merger or consolidation). The Company shall not be required (i) to transfer on its books any of the Restricted Shares which have been transferred in violation of any of the provisions of this Agreement or (ii) to treat as owner of such Restricted Shares or to pay dividends to any transferee to whom such Restricted Shares have been transferred in violation of any of the provisions of this Agreement.

5. Restrictive Legends.

The book entry account reflecting the issuance of the Restricted Shares in the name of the Participant shall bear a legend or other notation upon substantially the following terms:

“These shares of stock are subject to forfeiture provisions and restrictions on transfer set forth in a certain Restricted Stock Agreement between the corporation and the registered owner of these shares (or his or her predecessor in interest), and such Agreement is available for inspection without charge at the office of the Secretary of the corporation.”

6. Rights as a Shareholder.

Except as otherwise provided in this Agreement, for so long as the Participant is the registered owner of the Restricted Shares, the Participant shall have all rights as a shareholder with respect to the Restricted Shares, whether vested or unvested, including, without limitation, any rights to receive dividends and distributions with respect to the Restricted Shares and to vote the Restricted Shares and act in respect of the Restricted Shares at any meeting of shareholders. Notwithstanding the foregoing, any dividends, whether in cash, stock or property, declared and paid by the Company with respect to unvested Restricted Shares (“Accrued Dividends”) shall be paid to the Participant, without interest, only if and when such Restricted Shares vest.

7. Provisions of the Plan.

This Agreement is subject to the provisions of the Plan, a copy of which is furnished to the Participant with this Agreement. As provided in the Plan, upon the occurrence of a Reorganization Event (as defined in the Plan), the rights of the Company hereunder (including the right to receive forfeited Restricted Shares) shall inure to the benefit of the Company’s successor and, unless the Board determines otherwise, shall apply to the cash, securities or other property which the Restricted Shares were converted into or exchanged for pursuant to such Reorganization Event in the same manner and to the same extent as they applied to the Restricted Shares under this Agreement.

8. Tax Matters.

(a) Acknowledgments; Section 83(b) Election. The Participant acknowledges that he or she is responsible for obtaining the advice of the Participant’s own tax advisors with respect to the acquisition of the Restricted Shares and the Participant is relying solely on such advisors and not on any statements or representations of the Company or any of its agents with respect to the tax consequences relating to the Restricted Shares. The Participant understands that the Participant (and not the Company) shall be responsible for the Participant’s tax liability that may arise in connection with the acquisition, vesting and/or disposition of the Restricted Shares and any Accrued Dividends with respect to such Restricted Shares. The Participant acknowledges that he or she has been informed of the availability of making an election under Section 83(b) of the Internal Revenue Code, as amended, with respect to the issuance of the Restricted Shares and that the Participant has decided not to file a Section 83(b) election.

(b) Withholding. The Participant acknowledges and agrees that the Company has the right to deduct from payments of any kind otherwise due to the Participant any federal, state, local or other taxes of any kind required by law to be withheld with respect to the vesting of the Restricted Shares. On each date on which Restricted Shares vest, the Company shall deliver written notice to the Participant of the amount of withholding taxes due with respect to the vesting of the Restricted Shares that vest on such date; provided, however, that the total tax withholding cannot exceed the Company’s minimum statutory withholding obligations (based on minimum statutory withholding rates for federal and state tax purposes, including payroll taxes, that are applicable to such supplemental taxable income). The Participant shall satisfy such tax withholding obligations by transferring to the Company, on each date on which Restricted Shares vest under this Agreement, such number of Restricted Shares that vest on such date as have a fair market value (calculated using the last reported sale price of the common stock of the Company on the NASDAQ National Market on the trading date immediately prior to such vesting date) equal to the amount of the Company’s tax withholding obligation in connection with the vesting of such Restricted Shares. Such delivery of Restricted Shares to the Company shall be deemed to happen automatically, without any action required on the part of the Participant, and the Company is hereby authorized to take such actions as are necessary to effect such delivery.

9. Miscellaneous.

(a) Authority of Compensation Committee. In making any decisions or taking any actions with respect to the matters covered by this Agreement, the Compensation Committee shall have all of the authority and discretion, and shall be subject to all of the protections, provided for in the Plan. All decisions and actions by the Compensation Committee with respect to this Agreement shall be made in the Compensation Committee’s discretion and shall be final and binding on the Participant.

(b) No Right to Continued Employment. The Participant acknowledges and agrees that, notwithstanding the fact that the vesting of the Restricted Shares is contingent upon his or her continued employment by the Company, this Agreement does not constitute an express or implied promise of continued employment or confer upon the Participant any rights with respect to continued employment by the Company.

(c) Governing Law. This Agreement shall be construed, interpreted and enforced in accordance with the internal laws of the State of Delaware without regard to any applicable conflicts of laws provisions.

(d) Participant’s Acknowledgments. The Participant acknowledges that he or she has read this Agreement, has received and read the Plan, and understands the terms and conditions of this Agreement and the Plan.