Ko Yao Yai (island) is the largest island in the Ko Yao Archipelago. The island group is situated in the Phang Nga Bay in the Phang Nga province of Thailand. Ko Yao Yai means Big Yao Island. The other main island of the group is Ko Yao Noi (Little Yao Island), located off Ko Yao Yai's northern side and separated from it by a narrow sound.
The population of Ko Yao Yai is about 8,000, whereas the population of Ko Yao Noi is about 4,500. The area of the archipelago is 137,6 km2.