Sussex House School (commonly known as Sussex House), is a boys’ preparatory school located in Chelsea, London. Founded in 1952, the school occupies a house designed by Norman Shaw at 68 Cadogan Square, and since 1994 has operated as an independent charitable trust. It typically has a roll of between 180 and 190 pupils.

Affiliated to the Church of England, pupils use nearby St Simon Zelotes as the school chapel. Sussex House offers a variety of sports but is known in particular for its success in fencing. The headmaster maintains links with Eton, KCS Wimbledon, St Paul's, Westminster School, and Winchester College; in any given year around 80 per cent of leavers depart for one of these institutions.

Former pupils are known as Old Cadogans and include actor Daniel Radcliffe, author Edward St Aubyn, gerontologist Aubrey de Grey, senior politician Thomas Galbraith, 2nd Baron Strathclyde, and filmmaker Matthew Vaughn.