Longworth is a village and civil parish, located near Kingston Bagpuize and Southmoor, in the English county of Oxfordshire (formerly in Berkshire). It is in the Vale of White Horse district. In the 2001 census, Longworth had a population of 848.
Longworth parish extends north of the village to the River Thames, and the south of the parish includes part of the neighbouring village of Southmoor. Harrowdown Hill, in the north of the parish near the Thames, is where biological warfare expert, David Kelly, died (or committed suicide) during the Second Gulf War WMD scandal. Sir Henry Marten, a 17th century Judge of the Admiralty Court, and his son, Henry Marten, the infamous regicide, resided at Longworth House.