Ko Pha-ngan (Thai: เกาะพะงัน, RTGS: Ko Pha-ngan, pronounced [kɔ̀ʔ pʰā.ŋān]) is an island in the Gulf of Thailand in Surat Thani Province of southern Thailand. Ko Pha-ngan has two sister islands: the larger Ko Samui to the south and the smaller Ko Tao to the north. The main town is Thong Sala.

The name Ko Pha-ngan derives from the word "ngan", meaning "sandbar" in southern Thai. There are many sandbars offshore.^{[citation needed]}

Ko Pha-ngan has been a longtime favorite of past kings of Thailand. King Chulalongkorn (King Rama V) visited Ko Pha-ngan 14 times during his reign.

The Bronze Drum of Dongson Culture (500–100 BCE) that was found on Ko Samui in 1977 is evidence that there were settlements of people on Ko Samui, Ko Pha-ngan, and their islets more than 2,000 years ago. Some historians and archaeologists believe that the first group to migrate to Ko Pha-ngan were Austronesian peoples who traveled by boat from the Malay Peninsula.

Motorbikes are a major means of travel on Ko Pha-ngan.

Ko Pha-ngan is connected to Ko Samui, Ko Tao, and the mainland by regular ferry and speedboat services. Sea transportation remains the main way for visitors to travel to and from the island.

There used to be an option to reach Ko Pha-ngan by car ferry from Ko Samui (Raja Ferry Port, which is 9 km (5.6 mi) from Ko Pha-ngan) and from Donsak on the mainland.

Since 2012 Kannithi Aviation (Kan Air) has attempted to construct Ko Pha-ngan Airport on the island. Kan Air has spent 500 million baht to acquire about 32 ha (79 acres) of land to build a passenger terminal capable of handling 1,000 passengers a day and a 1,095 m (3,593 ft) runway to accommodate turboprop aircraft such as Kan Air's ATR 72-600 series. The project, originally estimated at 900 million baht, now estimated to cost two billion baht, has faced inflated costs, delays resulting from the yet-to-be-issued environmental impact assessment, and other complications, which pushed back initial plans to open in 2014.