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WASHINGTON, D.C.
WEST PALM BEACH
                                  May 15, 2002

Alliant Energy Corporation
4902 North Biltmore Lane
Madison, Wisconsin  53718-2132

Ladies and Gentlemen:

          We have acted as counsel for Alliant Energy Corporation, a Wisconsin
corporation (the "Company"), in conjunction with the preparation of a
Registration Statement on Form S-8 (the "Registration Statement") to be filed by
the Company with the Securities and Exchange Commission under the Securities Act
of 1933, as amended (the "Securities Act"), relating to 4,000,000 shares of the
Company's Common Stock, $.01 par value (the "Common Stock"), and related Common
Share Purchase Rights (the "Rights"), which may be issued or acquired pursuant
to the Alliant Energy Corporation 2002 Equity Incentive Plan (the "Plan"). The
terms of the Rights are as set forth in that certain Rights Agreement, dated as
of January 20, 1999, by and between the Company and U.S. Bank National
Association (formerly known as Firstar Bank, N. A.) (the "Rights Agreement").

          As such counsel, we have examined: (i) the Plan; (ii) the Registration
Statement; (iii) the Rights Agreement; (iv) the Company's Restated Articles of
Incorporation and By-Laws, as amended to date; (v) resolutions of the Company's
Board of Directors relating to the Plan and the issuance of securities
thereunder; and (vi) such other documents and records as we have deemed
necessary to enable us to render this opinion.

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

          1. The Company is a corporation validly existing under the laws of the
State of Wisconsin.

          2. The shares of Common Stock, when issued by the Company pursuant
to the terms and conditions of the Plan and subject to the effectiveness of the
Plan on May 16, 2002, will be validly issued, fully paid and nonassessable and
no personal liability will attach to the ownership thereof, except with respect
to wage claims of, or other debts owing to, employees of the Company for
services performed, but not exceeding six months' service in any one case, as
provided in Section 180.0622(2)(b) of the Wisconsin Business Corporation Law and
judicial interpretations thereof.

FOLEY & LARDNER
777 EAST WISCONSIN AVENUE, SUITE 3800
MILWAUKEE, WISCONSIN  53202-5367

TEL: 414.271.2400
FAX: 414.297.4900
WWW.FOLEYLARDNER.COM


FOLEY & LARDNER

Alliant Energy Corporation
May 15, 2002
Page 2

          3. The Rights when issued pursuant to the terms of the Rights
Agreement will be validly issued.

          We consent to the use of this opinion as an exhibit to the
Registration Statement. In giving our consent, we do not admit that we are
"experts" within the meaning of Section 11 of the Securities Act or within the
category of persons whose consent is required by Section 7 of the Securities
Act.

                                        Very truly yours,

                                        /s/ Foley & Lardner

                                        FOLEY & LARDNER