Khao Sam Roi Yot National Park is a marine national park in Kui Buri District, Prachuap Khiri Khan Province, Thailand. It covers 98.08 km2 (37.87 sq mi; 61,300 rai), of which 20.88 km2 (8.06 sq mi; 13,050 rai) are marine areas. The park was established in 1966, and was the first coastal national park of Thailand. The park includes Thailand's largest freshwater marsh.
The limestone hills are a sub-range of the Tenasserim Hills that arise at the shore of the Gulf of Thailand, with the highest elevation being Khao Krachom at 605 meters (1,985 ft). Between the hills are freshwater marshes.