POWER OF ATTORNEY

        Know all by these presents, that the undersigned hereby authorizes
Douglas T. Sheehy and Robert Lawson of Codexis, Inc. (the "Company"), and each
of them individually to execute for and on behalf of the undersigned, in the
undersigned's capacity as a director of the Company, Forms 3, 4 and 5, and any
amendments thereto, and cause such form(s) to be filed with the U.S. Securities
and Exchange Commission (the "SEC") pursuant to Section 16(a) of the Securities
Act of 1934, as amended (the "1934 Act") relating to the undersigned's
beneficial ownership of securities in the Company. 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 1934 Act.

        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.

        IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to
be executed as of this 18th day of February, 2011.

                                        /s/ Byron L. Dorgan
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                                        Byron L. Dorgan