Khao Sam Roi Yot National Park is a marine national park in Kui Buri District, Prachuap Khiri Khan Province, Thailand. It covers 61,300 rai~ 98 square kilometres of which 13,050 rai~ 21 square kilometres 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.