Koh Tonsay is located about 4.5 kilometers southeast of Kep. Tourists are drawn to the two beautiful white sand beaches. The sea here is shallow and has a long slope, making Koh Tonsay excellent for swimming. At the sea bottom are a variety of corals, sea animals and plants which attract researchers and ecologists.

The name Koh Tonsay is derived from the word Rumsay. While trying to avoid the commander’s troop, Prince Sakor Reach grew hopeless because his own troops began to tire. He led his remaining troops across the sea to an island in front of Kep city, where the troops spread out. Accordingly, the island was called Koh Rumsay, then Koh Ormsay or Koh Ornsay, and then Koh Tonsay, as it is known today.

Koh Tonsay is 2 square kilometers. During then-Prince Norodom Sihnouk’s Sangkum Reastr Niyum regme, it was used as a place to rehabilitate criminals, who were also used to defend the island. Horse cart paths and wooden, thatch roofed motels were also constructed during this time. Most of this infrastructure has been destroyed by weather and decades of war. Today, seven families live on the island. They earn their living by fishing and growing coconut trees.