EXHIBIT 5.1

                              Dickinson Wright PLLC
                         500 Woodward Avenue, Suite 4000
                             Detroit, Michigan 48226

                            Telephone (313) 223-3500
                               Fax (313) 223-3598

                               September 18, 2003


Securities and Exchange Commission
450 Fifth Street, N.W.
Judiciary Plaza
Washington, D.C. 20549

           Re:    Mercantile Bank Corporation
                  Registration Statement on Form S-3

Ladies and Gentlemen:

                  We represent Mercantile Bank Corporation, a Michigan
corporation (the "Company"), with respect to the above-captioned registration
statement on Form S-3 (the "Registration Statement") filed pursuant to the
Securities Act of 1933 (the "Act") to register 224,606 shares of the Company's
common stock ("Common Stock").

                  As counsel for the Company, we are familiar with its Articles
of Incorporation and Bylaws and have reviewed the various proceedings taken by
the Company to authorize the issuance of the Common Stock to be sold pursuant to
the Registration Statement. We have also reviewed and assisted in preparing the
Registration Statement. In our review, we have assumed the genuineness of all
signatures, the legal capacity of all natural persons, the authenticity of all
documents submitted to us as originals, the conformity to original documents of
all documents submitted to us as certified or photo static copies and the
authenticity of the originals of such copies.

                  On the basis of the foregoing, we are of the opinion that when
the Registration Statement has become effective under the Act, any and all
shares of Common Stock that are the subject of the Registration Statement will,
when issued upon payment of the purchase price therefore to the Company, be
validly issued, fully paid and nonassessable.





Securities and Exchange Commission
September 18, 2003
Page 2


         We consent to the use of this opinion as an exhibit to the Registration
Statement on Form S-3 covering the Common Stock to be issued, and to the use of
our name under the heading "Legal Matters" in the prospectus included in the
Registration Statement.

                                            Very truly yours,

                                            /s/ Dickinson Wright PLLC