FORM 4
[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).         
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES
                                                                                  
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      

1. Name and Address of Reporting Person *

Mason Michael 		2. Issuer Name and Ticker or Trading Symbol

ALNYLAM PHARMACEUTICALS, INC. [ ALNY ] 		5. Relationship of Reporting Person(s) to Issuer (Check all applicable)

_____ Director                      _____ 10% Owner
__ X __ Officer (give title below)      _____ Other (specify below)
VP, Finance and Treasurer
(Last)          (First)          (Middle)

300 THIRD STREET 		3. Date of Earliest Transaction (MM/DD/YYYY)

1/4/2018
(Street)

CAMBRIDGE, MA 02142
(City)        (State)        (Zip)
4. If Amendment, Date Original Filed (MM/DD/YYYY)

 
6. Individual or Joint/Group Filing (Check Applicable Line)

_ X _ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3) 		2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. Code
(Instr. 8) 		4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5) 		5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4) 		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V Amount (A) or (D) Price
Common Stock   1/4/2018     M (1)    1388   A $42.22   6352   D    
Common Stock   1/4/2018     M (1)    1667   A $63.0   8019   D    
Common Stock   1/4/2018     M (1)    3600   A $88.95   11619   D    
Common Stock   1/4/2018     M (1)    2750   A $96.45   14369   D    
Common Stock   1/4/2018     M (1)    2750   A $96.45   17119   D    
Common Stock   1/4/2018     M (1)    10000   A $97.72   27119   D    
Common Stock   1/4/2018     M (1)    6187   A $96.45   33306   D    
Common Stock   1/4/2018     M (1)    3439   A $63.0   36745   D    
Common Stock   1/4/2018     S (1)    5249   D $130.42   (2) 31496   D    
Common Stock   1/4/2018     S (1)    16500   D $131.2   (3) 14996   D    
Common Stock   1/4/2018     S (1)    12405   D $132.18   (4) 2591   D    
Common Stock   1/4/2018     S (1)    1591   D $132.98   (5) 1000   D    
Common Stock   1/4/2018     S (1)    400   D $133.83   (6) 600   D    
Common Stock   1/4/2018     S (1)    600   D $135.0   (7) 0   D    
Common Stock                  226   I   by Managed Account   (8)

Table II - Derivative Securities Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3) 		2. Conversion or Exercise Price of Derivative Security 3. Trans. Date 3A. Deemed Execution Date, if any 4. Trans. Code
(Instr. 8) 		5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5) 		6. Date Exercisable and Expiration Date 7. Title and Amount of Securities Underlying Derivative Security
(Instr. 3 and 4) 		8. Price of Derivative Security
(Instr. 5) 		9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Performance Stock Option 2013 (right to buy)   $63.0   1/4/2018     M   (1)       1667    9/20/2017   12/17/2023   Common Stock   1667   $0.0   0   D    
Performance Stock Option 2014 (right to buy)   $96.45   1/4/2018     M   (1)       2750    2/1/2016   12/17/2024   Common Stock   2750   $0.0   2750   D    
Performance Stock Option 2014 (right to buy)   $96.45   1/4/2018     M   (1)       2750    7/7/2017   12/17/2024   Common Stock   2750   $0.0   0   D    
Stock Option (right to buy)   $42.22   1/4/2018     M   (1)       1388      (9) 12/20/2026   Common Stock   1388   $0.0   4162   D    
Stock Option (right to buy)   $63.0   1/4/2018     M   (1)       3439      (9) 12/18/2023   Common Stock   3439   $0.0   0   D    
Stock Option (right to buy)   $88.95   1/4/2018     M   (1)       3600      (9) 12/18/2025   Common Stock   3600   $0.0   3600   D    
Stock Option (right to buy)   $96.45   1/4/2018     M   (1)       6187      (9) 12/17/2024   Common Stock   6187   $0.0   2063   D    
Stock Option (right to buy)   $97.72   1/4/2018     M   (1)       10000    12/7/2015   12/7/2025   Common Stock   10000   $0.0   0   D    

Explanation of Responses:
(1)  All sales reported on this Form 4 were made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on October 2, 2017.
(2)  Sale prices ranged from $129.74 to $130.72.
(3)  Sale prices ranged from $130.74 to $131.73.
(4)  Sale prices ranged from $131.75 to $132.71.
(5)  Sale prices ranged from $132.75 to $133.71.
(6)  Sale prices ranged from $133.78 to $134.11.
(7)  Sale prices ranged from $134.94 to $135.10
(8)  The reporting person owns 226 shares of ALNY common stock under the ALNY 401(k) plan as a result of the ALNY 401(k) matching contribution program.
(9)  The stock option vests as to 25% of the shares on the 1st anniversary of the date of the stock option grant and as to an additional 6.25% of the shares each successive three month period thereafter.

Reporting Owners
Reporting Owner Name / Address
Relationships
Director 10% Owner Officer Other
Mason Michael
300 THIRD STREET
CAMBRIDGE, MA 02142

VP, Finance and Treasurer

Signatures
/s/ Michael P. Mason 1/8/2018
** Signature of Reporting Person Date


Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.
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