Ownership Submission
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

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
GORMISKY PAUL J
   2. Issuer Name and Ticker or Trading Symbol
CABOT CORP [CBT] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
Vice President
(Last)
(First)
(Middle)
C/O CABOT CORPORATION, TWO SEAPORT LANE, SUITE 1300		 3. Date of Earliest Transaction (Month/Day/Year)
12/16/2005
(Street)

BOSTON, MA 02210		 4. If Amendment, Date Original Filed(Month/Day/Year)
 6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)		 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction 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 12/16/2005   S   400 D $ 34.72 87,821 D  
Common Stock 12/16/2005   S   100 D $ 34.73 87,721 D  
Common Stock 12/16/2005   S   500 D $ 34.76 87,221 D  
Common Stock 12/16/2005   S   600 D $ 34.82 86,621 D  
Common Stock 12/16/2005   S   400 D $ 34.85 86,221 D  
Common Stock 12/16/2005   S   100 D $ 34.86 86,121 D  
Common Stock 12/16/2005   S   700 D $ 34.87 85,421 D  
Common Stock 12/16/2005   S   200 D $ 34.88 85,221 D  
Common Stock 12/16/2005   S   1,000 D $ 34.89 84,221 D  
Common Stock               5,887.96 I Through the Trustee for the Corporation's Retirement Savings Plan

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)		 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction 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
(Month/Day/Year)		 7. Title and Amount of Underlying Securities
(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
Series B ESOP Convertible Preferred Stock (1)               (2)   (2) Common 2,083.05   14.23 I Through the Trustee for the Corporation's Retirement Savings Plan

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
GORMISKY PAUL J
C/O CABOT CORPORATION
TWO SEAPORT LANE, SUITE 1300
BOSTON, MA 02210		       Vice President  

Signatures

 Michaela Allbee, pursuant to a Power of Attorney from Paul Gormisky   12/20/2005
**Signature of Reporting Person Date

Explanation of Responses:

* 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).
(1) Each share is convertible into 146.3782 shares of the Corporation's common stock.
(2) Under the Retirement Savings Plan, the Corporation allocates Series B ESOP Convertible Preferred Stock to each participant's account on a quarterly basis. Subject to certain terms and conditions of the Retirement Savings Plan, participants may elect to receive distributions of their vested account balance in the form of shares of the Corporation's common stock or cash. Generally, a participant is 20% vested in his account after 2 years of service with the Corporation; 40% vested after 3 years of service; 60% vested after 4 years of service; and 100% vested after 5 years of service.

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.

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