Whitby—Ajax was a federal and provincial electoral district in Ontario, Canada.

It was represented in the House of Commons of Canada from 1997 to 2003, and in the Legislative Assembly of Ontario from 1999 to 2007.

It was located to the east of Toronto, consisting of the Town of Whitby and the part of the Town of Ajax lying to the south of Kingston Road.

The federal electoral district was abolished in 2003 when it was redistributed between Ajax—Pickering and Whitby—Oshawa ridings.

The provincial electoral district was abolished in 2007, when it was also redistributed into Ajax—Pickering and Whitby—Oshawa.