EXHIBIT 32.1

                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

     This certification is provided pursuant to Section 906 of the
Sarbanes-Oxley Act of 2002, 18 U.S.C. Section 1350, and accompanies the
quarterly report on Form 10-Q for the quarter ended September 30, 2005 (the
"Form 10-Q") of Mercantile Bank Corporation (the "Issuer").

     I, Gerald R. Johnson, Jr., Chairman and Chief Executive Officer of the
Issuer, certify that:

(i) the Form 10-Q fully complies with the requirements of Section 13(a) or
Section 15(d) of the Securities Exchange Act of 1934 (15 U.S.C. 78m(a) or
78o(d)); and

(ii) the information contained in the Form 10-Q fairly presents, in all material
respects, the financial condition and results of operations of the Issuer.

Dated: November 8, 2005


                                        /s/ Gerald R. Johnson, Jr.
                                        ----------------------------------------
                                        Gerald R. Johnson, Jr.
                                        Chairman and Chief Executive Officer


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