Filed Pursuant To Rule 433

Dated October 1, 2008

Registration Statement No. 333-151898

INTERSTATE POWER AND LIGHT COMPANY

Final Term Sheet

Dated October 1, 2008

Issuer:	Interstate Power and Light Company
Size:	$250,000,000
Security Type:	Senior Debentures
Maturity Date:	October 1, 2018
Interest Payment Dates:	April 1 and October 1, commencing April 1, 2009
Coupon:	7.25%
Price to Public	99.129%
Yield to Maturity:	7.375%
Benchmark Treasury:	4.00% due August 15, 2018
Benchmark Treasury Yield:	3.793%
Spread to Benchmark Treasury:	358.2 bps
Optional Redemption:	Make-whole call at T + 50 bps
Trade Date:	October 1, 2008
Settlement Date:	October 6, 2008 (T+3)
CUSIP:	461070 AF1
Underwriters:	Joint Book-Running Managers Barclays Capital Inc. Citigroup Global Markets Inc. J.P. Morgan Securities Inc. Co-Managers BNY Mellon Capital Markets, LLC Greenwich Capital Markets, Inc. Lazard Capital Markets LLC

The issuer has filed a registration statement (including a prospectus) with the SEC for the offering to which this communication relates. Before you invest, you should read the prospectus in that registration statement and other documents that the issuer has filed with the SEC for more complete information about the issuer and this offering. You may get these documents for free by visiting EDGAR on the SEC Web site at www.sec.gov. Alternatively, you may request a copy of these documents from Barclays Capital Inc. by calling (888) 227-2275, Ext. 2663, from Citigroup Global Markets Inc. by calling (877) 858-5407 or from J.P. Morgan Securities Inc. by calling (212) 834-4533.