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                                                                EX 4-1


COMMON STOCK                                                      COMMON STOCK

NUMBER KBI              KOSAN BIOSCIENCES INCORPORATED    SHARES

INCORPORATED UNDER THE LAWS
OF THE STATE OF DELAWARE                    SEE REVERSE FOR CERTAIN DEFINITIONS

                                                              CUSIP 50064W 10 7

This Certifies that




Is the record holder of

             FULLY PAID AND NON-ASSESSABLE SHARES OF COMMON STOCK, $.001 PAR
             VALUE, OF

-----------------------------KOSAN BIOSCIENCES INCORPORATED-------------------

transferable on the books of the Corporation by the holder hereof in person
or by duly authorized attorney, upon surrender of this Certificate properly
endorsed.  This certificate is not valid until countersigned and registered
by the Transfer Agent and Registrar.

    IN WITNESS WHEREOF the Corporation has caused this certificate to be
signed in facsimile by its duly authorized officers and a facsimile of its
corporate seal.

Dated:

/s/ MICHAEL S. OSTRACH           [SEAL]     /s/ DANIEL V. SANTI
----------------------------               ---------------------------
CHIEF OPERATING OFFICER AND                CHAIRMAN AND CHIEF EXECUTIVE
ASSISTANT SECRETARY                        OFFICER

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                      KOSAN BIOSCIENCES INCORPORATED

THE CORPORATION WILL FURNISH WITHOUT CHARGE TO EACH STOCKHOLDER WHO SO
REQUESTS, A FULL STATEMENT OF THE DESIGNATIONS, RELATIVE RIGHTS, PREFERENCES
AND LIMITATIONS OF EACH CLASS OF STOCK OR SERIES THEREOF AUTHORIZED TO BE
ISSUED AND THE AUTHORITY OF THE BOARD OF DIRECTORS OF THE CORPORATION TO
DESIGNATE AND FIX THE RELATIVE RIGHTS, PREFERENCES AND LIMITATIONS OF CLASSES
OF PREFERRED STOCK IN SERIES.

The following abbreviations, when used in the inscription on the face of this
certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

    TEN COM - as tenants in common
    TEN ENT - as tenants by the entireties
    JT WROS - as joint tenants with right of survivorship
              and not as tenants in common

UNIF GIFT MIN ACT - _________________ Custodian ________________
                         (Cust)                      (Minor)
                 under Uniform Gifts to Minors Act _____________
                                                      (State)

      Additional abbreviations may also be used though not in the above list.

For value received,                     hereby sell, assign and transfer unto
                   --------------------

PLEASE INSERT SOCIAL SECURITY OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE
-------------------------
/                        /
-------------------------

-------------------------------------------------------------------------------
(Please print or typewrite name and address including postal zip code of
assignee)

-------------------------------------------------------------------------------

-------------------------------------------------------------------------------

------------------------------------------------------------------------ Shares

of the Common Stock represented by the within Certificate, and do hereby
irrevocably constitute and appoint
                                  --------------------------------------------

----------------------------------------------------------------------
Attorney to transfer the said Shares on the Books of the within-named
Corporation with full power of substitution in the premises.

Dated:
      -----------------------------------------


                          ----------------------------------------------------
                          NOTICE:  The signature to this assignment must
                          correspond with the name as written upon the face of
                          the certificate in every particular, without
                          alteration or enlargement, or any change whatever.

SIGNATURE(S) GUARANTEED:
                          ----------------------------------------------------
                          THE SIGNATURE(S) MUST BE GUARANTEED BY AN ELIGIBLE
                          GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS
                          AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH
                          MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE
                          MEDALLION PROGRAM), PURSUANT TO S.E.C. RULE 17Ad-15.