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 June 30, 2003 (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: August 7, 2003

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