Ko Pha Ngan (or Koh Phangan, Thai: เกาะพะงัน, rtgs: Ko Pha-ngan, Thai pronunciation: [kɔ̀ʔ pʰa.ŋan]) is an island in the Gulf of Thailand in southeast Thailand in Surat Thani Province. It is part of the Samui Archipelago. It is famous for its Full Moon Party at Haad Rin Beach and as a backpacker destination. Ko Pha Ngan has two sister islands: the larger Ko Samui to the south and the smaller Ko Tao to the north.
- Estimated perimeter: 40 km (estimate-10 hr average walking time)
- From mainland: about 55 km
- From Ko Samui: about 15 km
- From Ko Tao: about 35 km
- Main town: Thong Sala
- Highest Point: Khao Ra, 630 m
Ko Pha Ngan has only 1 international primary school, Si Panya School in Baan Tai. Si Panya is a private primary school which follows the British national curriculum for girls and boys aged 5–12 years old. It was established in March 2012. Its opening was welcomed by many families as a necessary educational amenity, although some saw this as the first step towards overdevelopment of the island. An airport is currently (Dec 2014) under construction.