Koh Tonsay (Khmer: កោះទន្សាយ) is a Cambodian island located off the country's southern coast in the Gulf of Thailand.

[1] The island is open for visitors and tourists, who value white sand beaches and the marine scenery.

A number of coral reefs and a variety of habitats for animals and plants attract researchers and ecologists.

Currently there are individually built and run guest houses on the main beach, attracting Cambodian and foreign tourists.

Local settlers - fishermen and their families also live on the island, occupying other beaches around the shoreline.