Emerald Cave (Thai: ถ้ำมรกต, RTGS: Tham Morakot, pronounced [tʰâm mɔ̄ː.rā.kòt]) is a cave located on the west coast of Ko Muk (also known as Ko Mook) Island.

The paradise island of Ko Muk and Emerald Cave are part of the Trang Provence, Southern Thailand.

The cave can be entered either by swimming or by using a kayak.

Outside the cave, there is a lagoon which is surrounded by tropical plants and a beach.

The name of the cave is derived from the phenomenon that occurs, when the sun shines on the water, which reflects colored light all over the cave's wall.