Khao Sam Roi Yot (Thai: เขาสามร้อยยอด) 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.