Ko Yao (Thai: เกาะยาว, pronounced [kɔ̀ʔ jāːw]) is a district (amphoe) in Phang Nga province in Thailand's south.

Cave paintings discovered on Ko Yao Island, dating back over 2,000 years, provide evidence of historical influences on the communities in the southern mainland provinces of Thailand.

In addition to the Moken, the region has seen the migration of various nomadic peoples from the Malay Peninsula, believed to have settled on the islands between the 17th and 18th centuries.

[1][2] The Mon people, part of the Khmer ethnolinguistic group, established settlements in peninsular Thailand, including maritime states like Ligor (Nakhon Si Thammarat).

This integration has resulted in the Mon ethnic lineage being a prominent component of the demographic makeup in southern Thailand, including the population of Ko Yao.