EXHIBIT 21

ALLIANT ENERGY CORPORATION

SUBSIDIARIES OF THE REGISTRANT

The following are deemed to be significant subsidiaries of Alliant Energy Corporation as of Dec. 31, 2005:

Name of Subsidiary State or Country of Incorporation

Interstate Power and Light Company Iowa

Wisconsin Power and Light Company Wisconsin

Alliant Energy Resources, Inc. Wisconsin

Alliant Energy International, Inc. Iowa

Alliant Energy Holdings do Brasil Limitada Brazil

WISCONSIN POWER AND LIGHT COMPANY

SUBSIDIARIES OF THE REGISTRANT

The following are deemed to be significant subsidiaries of Wisconsin Power and Light Company as of Dec. 31, 2005:

Name of Subsidiary State of Incorporation

WPL Transco LLC Wisconsin