SecProbe.io

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549-7010

       DIVISION OF
CORPORATION FINANCE

Mail Stop 7010
March 28, 2008
 Via U.S. mail and facsimile

 Mr. Patrick M. Prevost Chief Executive Officer Cabot Corporation
Two Seaport Lane, Suite 1300
Boston, MA  02210

 RE: Form 10-K for the fiscal year ended September 30, 2007
File No. 001-05667

Dear Mr. Prevost:    We have reviewed your filings and have the following comments.  If you disagree with a comment, we will consider your explanation as to why our comment is inapplicable or a revision is unnecessary.  Pl ease be as detailed as necessary in your
explanation.  In some of our comments, we may ask you to provide us with information so we may better understand your disclosure.  After reviewing this information, we may
or may not raise additional comments.   Please understand that the purpose of our re view process is to assist you in your
compliance with the applicable disclosure  requirements and to  enhance the overall
disclosure in your filing.  We look forward to  working with you in these respects.  We
welcome any questions you may have about our comments or on any other aspect of our review.  Feel free to call us at the telephone numbers listed at the end of this letter.

FORM 10-K FOR THE YEAR ENDED SEPTEMBER 30, 2007

General
1. Where a comment below requests additional disclosures or other revisions to be
made, please show us in your supplemental response what the revisions will look like.
These revisions should be included in your future filings, including your interim
filings.

Mr. Patrick M. Prevost
Cabot Corporation
March 28, 2008 Page 2    Business

Sales and Customers, page 8
2. Please identify the silicone and microelectr onics customers who represent a material
portion of the Metal Oxides business sales.  Please also identify the four material
capacitor customers mentioned on page 9.  We note from your risk factor disclosure
that the loss of any one or more of th ese customers could materially affect your
business.

Legal Proceedings
 Environmental Proceedings, page 20

3. Please either delete the statement in th e third full paragraph on page 21 that you
believe the claims are without merit or e xplain why you think they are without merit.
 Other Proceedings

 Respirator Liabilities, page 21

4. Please disclose the amount by which your tota l costs and payments have exceeded the
amount you received from Aearo.
 Management’s Discussion and Analysis of Fi nancial Condition and Results of Operations

Fiscal Year 2007 compared to Fiscal Year s 2006 and 2005 – By Business Segment, page
40
5. Your presentation of total segment operating profit before taxes (PBT) constitutes a
non-GAAP measure when it appears outside of your segment footnote.  Please revise
your filing to clearly identif y total segment PBT as a non-GAAP measure and provide
a statement disclosing the reasons why mana gement believes that the presentation of
the non-GAAP financial measure provide usef ul information to investors regarding
your results of operations.  For additional gui dance, refer to Item 10(e) of Regulation
S-K and Question 21 of our Frequently As ked Questions Regarding the Use of Non-
GAAP Financial Measures, which was released on June 13, 2003.
6. As a related matter, please revise your di scussion on segment MD &A to address the
business reasons for changes between periods  in the certain items expense line item
that you present in your segment fo otnote and in the table on page 41.

Mr. Patrick M. Prevost
Cabot Corporation
March 28, 2008 Page 3    Consolidated Financial Statements

Note Q – Earnings Per Share, page 92
7. Please revise your filing to clarify whether the basic EPS adjustment to reduce
weighted-average common shares outstandi ng for contingently issuable shares (3
million shares for each period presented) is  intended to represent the effect of
outstanding unvested restri cted stock, vested re stricted stock or both.
 Note S – Commitments and Contingencies, page 96

8. Please disclose how you account for (a) step  rent provisions and escalation clauses
and (b) capital improvement funding and other lease concessions, which may be
present in your leases.  In addition, pa ragraph 5.n. of SFAS 13, as amended by SFAS
29, discusses how lease payments that depend on  an existing index or rate, such as the
consumer price index or the prime interest  rate, should be initi ally included in your
minimum lease payments.  If, as we assume, each of these items is included in computing your minimum lease payments and the minimum lease payments are recognized on a straight-line basis over the minimum lease term, the note should so
state.  If our assumption is incorrect, pl ease tell us how you considered the provisions
in SFAS 13 and FTB 88-1 in reaching the conclusions you did regarding your
accounting treatment.
9. We note your disclosure on page 34 that you ar e partially self-insur ed for certain third
party liability, workers’ compensation and employee health benefits in the United
States and Canada.  Please revise your filing here and on page 34 to disclose the
extent to which you have excess loss insura nce.  Your revise d disclosures should
quantify the thresholds at which the excess lo ss insurance coverage would take effect
for each risk (e.g. workers compensation, third party liability, etc) and should identify
the risks for which you have no excess loss coverage.

*    *    *    *
      Please respond to these comments with in 10 business days, or tell us when you
will provide us with a response.  Please provi de us with a response letter that keys your
responses to our comments and provides a ny requested information.  Detailed letters
greatly facilitate our review.  Pleas e furnish your response on EDGAR as a
correspondence file.  Please understand that we may have additional comments after reviewing your responses to our comments.

Mr. Patrick M. Prevost
Cabot Corporation March 28, 2008 Page 4
We urge all persons who are responsible for the accuracy and adequacy of the
disclosure in the filings reviewed by the staff to be certain that they have provided all information investors require for an info rmed decision.  Since the company and its
management are in possession of all facts re lating to a company’s disclosure, they are
responsible for the accuracy and adequacy of the disclosures they have made.

 In connection with responding to our comments, please provide, in writing, a statement from the company acknowledging that:
• the company is responsible for the adequacy and accuracy of the disclosure in
their filings;
• staff comments or changes to disclosure  in response to staff comments do not
foreclose the Commission from taking any action with respect to the filing; and
• the company may not assert staff comme nts as a defense in any proceeding
initiated by the Commission or any pers on under the federal s ecurities laws of
the United States.

  In addition, please be advi sed that the Division of En forcement has access to all
information you provide to the staff of the Divi sion of Corporation Fi nance in our review
of your filing or in response to our comments on your filing.
  You may contact Errol Sanderson, Financia l Analyst, at (202) 551-3746 or, in his
absence, Jennifer Hardy, Legal Branch Chief, at (202) 551-3767 if you have any
questions regarding legal matters.  Please cont act Lisa Haynes, Staff Accountant, at (202)
551-3424 or, in her absence, the undersigned at (202) 551-3769 if you have questions
regarding comments on the financial st atements and related matters.
          S i n c e r e l y ,              R u f u s  D e c k e r          A c c o u n t i n g  B r a n c h  C h i e f