Sylvia Olive Pleadwell Sayer, Lady Sayer (6 March 1904 – 4 January 2000), was a passionate conservationist and environmental campaigner on behalf of Dartmoor, an area of mostly granite moorland in Devon in the south-west of England. She was chairman of the Dartmoor Preservation Association from 1951 to 1973, and remained deeply involved with the organisation until her death.
Sayer's grandfather was Robert Burnard (1848–1920), who with Sabine Baring-Gould performed the first scientific excavations of ancient monuments on Dartmoor, including Grimspound; and who was one of the founding members in 1883 of the Dartmoor Preservation Association. He leased Huccaby House, on the West Dart River, near Hexworthy, from the Duchy of Cornwall and Sayer used to visit as a child.
Her mother was Olive Louise Munday (1873–1960), née Burnard, Robert Burnard's eldest daughter. Her father was the Principal Medical Officer at the Naval Hospital School in Greenwich. She attended Princess Helena College in Ealing, and then the Central School of Art in London. In 1925 she married Guy Sayer, who was a midshipman in the Royal Navy, and they spent some time in China. Three years later they bought Old Middle Cator, a dilapidated Dartmoor longhouse about two miles west of the village of Widecombe-in-the-Moor in Dartmoor. They had twin sons, Geoffrey and Oliver, born in 1930, and until World War Two the family travelled widely to meet the needs of Guy's navy career. After VE Day, Guy was posted to the Far East and Sylvia settled at Cator and became interested in local politics, at first as a parish councillor for Widecombe, then as a Rural District Councillor and a member of the Dartmoor Sub-Committee of Devon County Council.