Khao Yai National Park is the first national park in Thailand which is known as the heritage park of ASEAN. Furthermore, it is accepted as the most significant national park in the world. With the cooperation and aid from Dr. George C. Ruhle, the expert in national park from International Union for Conservation of Nature, there was the announcement for national park establishment noted in the royal decree to determine Khao Yai Forest in Pa Kha and Bann Phraw Sub-district in Bann Na District, Nong Sang and Na Hin Lad Sub-district in Bang Phli District, Sarika, Hin Tung, and Phrommanee Sub-district in Mueang District, Nakhon Nayok Province, Prachantakham Sub-district, Prachantakham District, Sum Phun Ta and Thung Pho Sub-district, Kabinburi District, Mu Si Sub-district, Pak Chong District, Nakhon Ratchasima Province, and Muak Lek and Sum Phak Saew Sub-district, Kang Khoi District, Saraburi Province, as the national park in 1959. This was announced in the Government Gazette, Copies 79, Section 86 dated 18 September 1962. The park covers 2,168,750,000 square meters.