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American Financial Group, Inc.
June 29, 1999
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                                                                     EXHIBIT 5.1

                                [KMK Letterhead]






PAUL V. MUETHING
DIRECT DIAL: (513)579-6517
FACSIMILE: (513)579-6956
E-MAIL: PMUETHING@KMKLAW.COM



                                  June 29, 1999


American Financial Group, Inc.
One East Fourth Street
Cincinnati, Ohio 45202

Ladies and Gentlemen:

         We have acted as counsel to American Financial Group, Inc., an Ohio
corporation (the "Company") and American Financial Capital Trust II, a Delaware
business trust (the "Trust") in connection with the registration under the
Securities Act of 1933 (the "Act"), pursuant to a registration statement on Form
S-3 (the "Registration Statement") of up to $500,000,000 of (i) shares of Common
Stock of the Company (the "Common Stock"); (ii) debt securities of the Company
(the "Debt Securities"); (iii) Preferred Securities of the Trust (the "Preferred
Securities"); and (iv) the guarantee by the Company (the "Guarantee") of certain
obligations of the Trust pursuant to the Preferred Securities and common
securities to be issued by the Trust, which Guarantee will be evidenced by
agreements in substantially the form attached or incorporated by reference as an
exhibit to the Registration Statement (collectively, the "Guarantee Agreement").
The Common Stock, Debt Securities, Guarantees and Preferred Securities are
herein collectively referred to as the "Offered Securities"). Capitalized terms
used but not defined herein have the respective meanings ascribed to them in the
Registration Statement.

         We have, as counsel, examined such corporate records, certificates of
public officials and officers of the Company and other documents and reviewed
such questions of law as we have deemed necessary or appropriate to enable us to
render the opinions expressed below. In rendering such opinions, we have assumed
the genuineness of all signatures and the authenticity of all documents examined
by us and the legal capacity of natural persons who are parties to the documents
examined by us. As to various questions of fact material to such opinions, we
have relied upon representations of the Company.

         In connection with the opinions expressed below, we have further
assumed that (i) the Board of Directors of the Company or, to the extent
permitted by the Ohio General Corporation Law, a duly


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American Financial Group, Inc.
June 29, 1999
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constituted and acting committee thereof (such Board of Directors or Committee
being referred to herein as the "Board") will have duly established the terms of
the applicable Offered Securities and duly authorized the issuance and sale of
such Offered Securities and such authorization will not have been modified or
rescinded; (ii) the Registration Statement, and any amendments thereto
(including post-effective amendments), will have become effective under the Act
and will not have been terminated or rescinded; (iii) a prospectus supplement as
contemplated by the Registration Statement will have been prepared and filed
with the Securities and Exchange Commission describing the Offered Securities
offered thereby; (iv) all Offered Securities will be issued and sold in
compliance with applicable federal and state securities laws and in the manner
stated in the Registration Statement and the appropriate prospectus supplement;
(v) there will not have occurred any change in the law affecting the validity or
enforceability of the Offered Securities; and (vi) a definitive purchase,
underwriting, sales agency or similar agreement with respect to the Offered
Securities will have been duly authorized and validly executed and delivered by
the Company and/or the Trust and the other parties thereto.

         Based upon the foregoing, and subject to the assumptions,
qualifications, limitations and exceptions set forth herein, we are of the
opinion that:

         1. When (i) the Board has taken all necessary corporate action to
approve the issuance and sale of the Common Stock and (ii) the Common Stock has
been duly issued and sold as contemplated by the Registration Statement and any
prospectus supplement, such shares of Common Stock will be validly issued, fully
paid and nonassessable.

         2. When (i) the terms of the Debt Securities and of their issuance and
sale have been duly established in conformity with the applicable Indenture in
substantially the form attached as an exhibit to the Registration Statement so
as not to violate any applicable law or result in a default under or breach of
any agreement or instrument binding upon the Company and so as to comply with
any requirement or restriction imposed by any court or governmental body having
jurisdiction over the Company; and (ii) the Debt Securities have been duly
executed and authenticated in accordance with the applicable Indenture and
issued and sold as contemplated in the Registration Statement and any prospectus
supplement, the Debt Securities will constitute valid and legally binding
obligations of the Company, enforceable in accordance with their terms, except
as the enforceability thereof may be limited by (a) bankruptcy, insolvency,
reorganization, fraudulent transfer, moratorium or other similar laws now or
hereafter in effect relating to or affecting the enforcement of creditor's
rights generally and (b) equitable principles of general applicability,
regardless of whether considered in a proceeding at law or in equity.

         3. When (i) the Guarantee Agreement has been validly executed and
delivered by the Company and (ii) the Preferred Securities of the Trust have
been duly issued and delivered by the


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American Financial Group, Inc.
June 29, 1999
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Trust as contemplated by the Registration Statement and any prospectus
supplement, the Guarantee will constitute valid and legally binding obligations
of the Company, enforceable in accordance with their terms, except as the
enforceability thereof may be limited by (a) bankruptcy, insolvency,
reorganization, fraudulent transfer, moratorium or other similar laws now or
hereafter in effect relating to or affecting the enforcement of creditor's
rights generally and (b) equitable principles of general applicability,
regardless of whether considered in a proceeding at law or in equity.

         This opinion is rendered solely to you in connection with the matters
described herein. This opinion may not be used or relied upon by you for any
other purpose or relied upon by or furnished to any other person without our
prior written consent, except as set forth below.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the references to this firm under the heading
"Legal Matters" in the prospectus included in the Registration Statement. In
giving such consent, we do not thereby admit that we come within the category of
persons whose consent is required under Section 7 of the Act or the rules and
regulations of the Securities and Exchange Commission thereunder.

                                           Yours truly,

                                           KEATING, MUETHING & KLEKAMP, P.L.L.



                                           BY:    /s/ Paul V. Muething
                                              --------------------------------
                                                      Paul V. Muething