Knowsley South was a constituency in Merseyside, represented in the House of Commons of the Parliament of the United Kingdom.

Sean Hughes of the Labour Party held the seat from its creation at the 1983 election until his death in June 1990.

This was a safe Labour seat for the entire period of its existence, with the party's share of the vote exceeding 68% at all six elections in that time.

The constituency covered the southern part of the metropolitan borough of Knowsley, including Halewood, Huyton, Prescot, Roby and Whiston.

This seat and its neighbour Knowsley North and Sefton East were abolished at the 2010 general election, following the decisions of the Boundary Commission for England.