FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person * PROTSCH ELIOT G   2. Issuer Name and Ticker or Trading Symbol ALLIANT ENERGY CORP [LNT] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) SENIOR EXEC VP & CFO (Last) (First) (Middle) PO BOX 2568 3. Date of Earliest Transaction (Month/Day/Year) 02/15/2007 (Street) MADISON, WI 53701 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price COMMON 02/15/2007   M   11,798 A $ 31.54 11,798 D   COMMON 02/15/2007   S   11,798 D $ 42.3633 0 D   COMMON 02/15/2007   M   16,642 A $ 27.79 16,642 D   COMMON 02/15/2007   S   16,642 D $ 42.3633 0 D   COMMON 02/15/2007   M   11,099 A $ 24.9 11,099 D   COMMON 02/15/2007   S   11,099 D $ 42.3633 0 D   COMMON 02/15/2007   M   7,071 A $ 29.875 7,071 D   COMMON 02/15/2007   S   7,071 D $ 42.3633 0 D   COMMON DRIP               7,098.7512 D   401(k)               18,435.4875 D   COMMON (RESTRICTED)               34,004.0915 D

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

EMP. STOCK OPTION (Right to Buy)

$ 24.9

02/15/2007

M

11,099

01/02/2005

01/02/2014

COMMON

11,099

$ 0

10,000

D

EMP. STOCK OPTION (Right to Buy)

$ 27.79

02/15/2007

M

16,642

05/16/2005

05/16/2012

COMMON

16,642

$ 0

10,000

D

EMP. STOCK OPTION (Right to Buy)

$ 29.875

02/15/2007

M

7,071

06/01/2002

06/01/2009

COMMON

7,071

$ 0

0

D

EMP. STOCK OPTION (Right to Buy)

$ 31.54

02/15/2007

M

11,798

01/02/2003

01/02/2011

COMMON

11,798

$ 0

0

D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
PROTSCH ELIOT G PO BOX 2568 MADISON, WI 53701			SENIOR EXEC VP & CFO

Signatures

F. J. Buri as POA for		02/16/2007
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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