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                                                                     EXHIBIT 5.1
                          Calfee, Haller & Griswold
                       1400 McDonald Investment Center
                             800 Superior Avenue
                         Cleveland, Ohio  44114-2688

                               September 28, 1995


National BancShares Corporation
c/o First National Bank Operations
 Center
112 West Market Street
Orrville, Ohio  44667


                 In connection with the filing by National Bancshares
Corporation, an Ohio corporation (the "Company"), with the Securities and
Exchange Commission under the provisions of the Securities Act of 1933, as
amended, of a Registration Statement on Form S-3 (the "Registration Statement")
with respect to 100,000 Common Shares, par value $10.00 per share of the Company
(the "Shares"), we have examined the following: (i) the Amended Articles of
Incorporation, as amended, and Code of Regulations, as amended, of the Company,
as the same are currently in effect; (ii) the form of Registration Statement on
Form S-3 (including Exhibits thereto) to be filed with the Securities and
Exchange Commission; and (iii) such other documents as we deemed it necessary to
examine as a basis for the opinions hereinafter expressed. The Shares are to be
issued pursuant to the Company's Dividend Reinvestment Plan (the "Plan") to
those shareholders of the Company who choose to participate in the Plan ("Plan
Participants").

                 Based upon the foregoing, we are of the opinion that:

                  (i)   The Company is incorporated and validly existing under
         the laws of the State of Ohio.

                  (ii)  The Shares to be sold by the Company in the manner
         contemplated by the Registration Statement have been duly authorized
         and, when issued to the Plan Participants in accordance with the terms
         of the Plan, will be legally issued, fully paid and non-assessable.

                  We are attorneys licensed to practice law in the State of
Ohio. The opinions expressed herein are limited solely to the laws of the State
of Ohio and we express no opinion under the laws of any other jurisdiction.

                  This opinion is delivered to you solely in connection with the
filing of the Registration Statement with respect to the Shares, and this letter
and the opinion stated herein may not be relied upon for any other purpose or by
any other person.


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                 We consent to the filing of this opinion with the Registration
Statement and to the use of our name therein under the caption "Validity of
Shares."
                                                   
                                                   Respectfully submitted,

                                                   /s/ Calfee, Halter & Griswold
                                                   CALFEE, HALTER & GRISWOLD