POWER OF ATTORNEY

	Know all by these presents, that the undersigned hereby
constitutes and appoints each of Jane A. Bell, Michaela
Allbee and Brian A. Berube, signing singly, the undersigned's
true and lawful attorney-in-fact to:

(1)	  execute for and on behalf of the undersigned, in the
undersigned's capacity as an officer and/or director of Cabot
Corporation (the "Company"), Forms 3, 4, and 5 in accordance
with Section 16(a) of the Securities Exchange Act of 1934 and
the rules thereunder;

(2)	  do and perform any and all acts for and on behalf of the
undersigned which may be necessary or desirable to complete
and execute any such Form 3, 4, or 5, complete and execute
any amendment or amendments thereto, and timely file such
form with the United States Securities and Exchange
Commission and any stock exchange or similar authority; and

(3)	  take any other action of any type whatsoever in
connection with the foregoing which, in the opinion of such
attorney-in-fact, may be of benefit to, in the best interest
of, or legally required by, the undersigned, it being
understood that the documents executed by such
attorney-in-fact on behalf of the undersigned pursuant to
this Power of Attorney shall be in such form and shall
contain such terms and conditions as such attorney-in-fact
may approve in such attorney-in-fact's discretion.

	The undersigned hereby grants to each such attorney-in-fact
full power and authority to do and perform any and every act
and thing whatsoever requisite, necessary, or proper to be
done in the exercise of any of the rights and powers herein
granted, as fully to all intents and purposes as the
undersigned might or could do if personally present, with
full power of substitution or revocation, hereby ratifying
and confirming all that such attorney-in-fact, or such
attorney-in-fact's substitute or substitutes, shall lawfully
do or cause to be done by virtue of this power of attorney
and the rights and powers herein granted.  The undersigned
acknowledges that the foregoing attorneys-in-fact, in serving
in such capacity at the request of the undersigned, are not
assuming, nor is the Company assuming, any of the
undersigned's responsibilities to comply with Section 16 of
the Securities Exchange Act of 1934.

	This Power of Attorney shall remain in full force and effect
until the undersigned is no longer required to file Forms 3,
4, and 5 with respect to the undersigned's holdings of and
transactions in securities issued by the Company, unless
earlier revoked by the undersigned in a signed writing
delivered to the foregoing attorneys-in-fact.  The
undersigned hereby revokes any previous powers of attorney
delivered to the Company concerning the subject matter
hereof.

	IN WITNESS WHEREOF, the undersigned has caused this Power of
Attorney to be executed as of this 11th day of June, 2003.


/s/ John S. Clarkeson
Signature





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