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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549



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FORM 10-Q/A

Amendment No. 1



(Mark One)

|x | QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934.
|- | ----------------------------------------------------------------------------------------



For the quarterly period ended March 31, 2004.



OR



| ̈ | TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934.
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For the transition period from
 to
.



Commission File Number:

000-31633



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Kosan Biosciences Incorporated

(Exact name of registrant as specified in its charter)



|                                                                        |  |                                                
|----------------------------------------------------------------------- |  | -----------------------------------------------
|Delaware (State or other jurisdiction of incorporation or organization) |  | 94-3217016 (I.R.S. Employer Identification No.)



3832 Bay Center
Place, Hayward, California 94545

(address of principal executive offices)



(510) 732-8400

(Registrants telephone number, including area code)



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Indicate by check mark whether the Registrant (1) has
filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 (the Exchange Act) during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports),
and (2) has been subject to such filing requirements for the past 90 days.  Yes  x  No ̈



Indicate by check mark
whether the Registrant is an accelerated filed (as defined in Rule 12b-2 of the Exchange Act). Yes  x  No ̈



Indicate the number of shares
outstanding of each of the issuers classes of common stock, as of the latest practicable date: Common Stock, $.001 par value; 28,922,010 shares outstanding at April 30, 2004.



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EXPLANATORY NOTE



This amendment on Form 10-Q/A amends Item 6 to Part II of the Quarterly Report of Kosan Biosciences Incorporated (the
Company) on Form 10-Q previously filed for the quarter ended March 31, 2004 (the Prior Report), and together these two filings constitute the Quarterly Report of the Company for the quarter ended March 31, 2004 and are
referred to herein as the quarterly report.



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PART II  OTHER INFORMATION



|Item 6. | Exhibits and Reports on Form 8-K
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(a) Exhibits



|           |  |                                                                                                                                                                                                                                                          
|---------- |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|ExhibitNo. |  |                                                                                                                                                                                                                                                          
|3.1        |  | Amended and Restated Certificate of Incorporation.(1)                                                                                                                                                                                                    
|3.2        |  | Amended and Restated Bylaws of Registrant.(2)                                                                                                                                                                                                            
|4.1        |  | Form of Specimen Common Stock Certificate.(3)                                                                                                                                                                                                            
|31.1       |  | Certification required by Rule 13a-14(a) or Rule 15d-14(a).                                                                                                                                                                                              
|31.2       |  | Certification required by Rule 13a-14(a) or Rule 15d-14(a).                                                                                                                                                                                              
|32.1       |  | Certification by the Chief Executive Officer and the Chief Financial Officer of Kosan Biosciences Incorporated, as required by Rule 13a-14(b) or Rule 15d-14(b) and Section 1350 of Chapter 63
of Title 18 of the United Stated Code (18 U.S.C. 1350).(4)



(b) Reports on Form
8-K



On February 26, 2004, we filed a Current
Report on Form 8-K, in connection with the announcement of the Companys financial results for the three and twelve months ended December 31, 2003.





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|(1) | Incorporated herein by reference to an exhibit of our Quarterly Report on Form 10-Q for the period ended June 30, 2001.
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|(2) | Incorporated herein by reference to an exhibit of our Quarterly Report on Form 10-Q for the period ended June 30, 2003.
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|(3) | Incorporated herein by reference to an exhibit of our Registration Statement on Form S-1, Registration No. 333-33732.
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|(4) | Previously filed with our Quarterly Report on Form 10-Q, which this Quarterly Report on Form 10-Q/A amends.
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SIGNATURES



Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this report to be signed on its behalf
by the undersigned, thereunto duly authorized.



|             |  |  |  |                                |  |                                                                                      
|------------ |  |  |  | ------------------------------ |  | -------------------------------------------------------------------------------------
|             |  |  |  | Kosan Biosciences Incorporated
|             |  |  | 
|May 18, 2004 |  |  |  | By:                            |  | /s/    Daniel V. Santi, M.D., Ph.D.                                                  
|             |  |  |  |                                |  |                                                                                      
|             |  |  |  |                                |  | Daniel V. Santi, M.D., Ph.D. Chairman and Chief
Executive Officer                    
|             |  |  | 
|May 18, 2004 |  |  |  | By:                            |  | /s/    Susan M. Kanaya                                                               
|             |  |  |  |                                |  |                                                                                      
|             |  |  |  |                                |  | Susan M. Kanaya Senior Vice President, Finance, Chief
Financial Officer and Secretary



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EXHIBIT INDEX



|           |  |                                                                                                                                                                                                                                                          
|---------- |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|ExhibitNo. |  |                                                                                                                                                                                                                                                          
|3.1        |  | Amended and Restated Certificate of Incorporation.(1)                                                                                                                                                                                                    
|3.2        |  | Amended and Restated Bylaws of Registrant.(2)                                                                                                                                                                                                            
|4.1        |  | Form of Specimen Common Stock Certificate.(3)                                                                                                                                                                                                            
|31.1       |  | Certification required by Rule 13a-14(a) or Rule 15d-14(a).                                                                                                                                                                                              
|31.2       |  | Certification required by Rule 13a-14(a) or Rule 15d-14(a).                                                                                                                                                                                              
|32.1       |  | Certification by the Chief Executive Officer and the Chief Financial Officer of Kosan Biosciences Incorporated, as required by Rule 13a-14(b) or Rule 15d-14(b) and Section 1350 of Chapter 63
of Title 18 of the United Stated Code (18 U.S.C. 1350).(4)

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|(1) | Incorporated herein by reference to an exhibit of our Quarterly Report on Form 10-Q for the period ended June 30, 2001.
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|(2) | Incorporated herein by reference to an exhibit of our Quarterly Report on Form 10-Q for the period ended June 30, 2003.
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|(3) | Incorporated herein by reference to an exhibit of our Registration Statement on Form S-1, Registration No. 333-33732.
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|(4) | Previously filed with our Quarterly Report on Form 10-Q, which this Quarterly Report on Form 10-Q/A amends.
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