EXHIBIT 32.1

CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350, AS ADOPTED PURSUANT
TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

     In connection with the Annual Report on Form 10-K of Alnylam Pharmaceuticals, Inc. (the “Company”) for the fiscal year ended December 31, 2009 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), the undersigned, John M. Maraganore, Ph.D., Chief Executive Officer of the Company, hereby certifies, pursuant to Section 1350 of Chapter 63 of Title 18, United States Code, that, to his knowledge:

(1)	the Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and
(2)	the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Dated: February 26, 2010	/s/ John M. Maraganore, Ph.D.
	John M. Maraganore, Ph.D.
	Chief Executive Officer