S. Thomas' Preparatory School (abbreviated as STPS) is a private, Anglican, multi-ethnic, primary and secondary day school for boys aged 5 to 16 years, located in Kollupitiya in the Colombo District of the Western Province of Sri Lanka. The school was founded on 17 May 1938 as a branch preparatory school of S. Thomas' College, Mount Lavinia. It is governed by the Board of Governors of S. Thomas' College of the Church of Ceylon. The school is amongst the elite schools of Sri Lanka and is affiliated with the three other Thomian schools and colleges administered by the Church of Ceylon.