Ko Samet (Thai: เกาะเสม็ด, Thai pronunciation: [kɔ̀ʔ samèt]) is one of the Eastern Seaboard Islands of Thailand. It is in the Gulf of Thailand off the coastline of the Thai province of Rayong, approximately 220 kilometres (140 mi) southeast of Bangkok. Ko Samet is part of the Phe (Thai: เพ) Subdistrict of the Amphoe Mueang Rayong (Thai: เมืองระยอง, the capital district, or Amphoe Mueang), of Rayong Province. Ko Samet is the largest and westernmost of a cluster of islands not far from the coast.