EXHIBIT 32

CERTIFICATIONS 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 filing of the Annual Report on Form 10-K for the year ended September 30, 2005 (the “Report”) by Cabot Corporation (the “Company”), each of the undersigned hereby certifies pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

      1. The Report fully complies with the requirements of section 13 (a) or 15 (d) of the Securities Exchange Act of 1934, as amended; and

      2. The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/ Kennett F. Burnes

Kennett F. Burnes

Chairman of the Board, President and Chief Executive Officer

December 13, 2005

/s/ John A. Shaw

John A. Shaw

Executive Vice President and

Chief Financial Officer

December 13, 2005