Ko Chang (Thai: เกาะช้าง, pronounced [kɔ̀ʔ tɕʰáːŋ], also Koh Chang) is an amphoe (district) in Trat Province, Thailand. It is located on the Gulf of Thailand's eastern seaboard, 310 km from Bangkok and near the border with Cambodia.

It is the country's third largest island, and the largest island in the Mu Ko Chang National Park archipelago.

The name means Elephant Island, and comes from the elephant shape of its headland, although elephants are not indigenous to the island. At present, there are 9 villages on the island.

It is a mountainous island, with Khao Salak Phet being the highest peak at 743 metres. The island is known for several waterfalls, thriving coral reefs and rainforests. The island has an area of approximately 217 square kilometers.