At the end of World War II, there was a series of attempts to establish national parks in Thailand, some of which were successful. These attempts were made following the rapid growth in population, which created economic pressure. Wildlife habitats were turned into human settlements and farm land. Fertile forests were encroached upon, cleared and afterwards abandoned, left to become derelict old clearings and degraded forests.

Wildlife was hunted for sale and for consumption. Some species came to the brink of extinction, while others disappeared forever. For these reasons, the Department of National Parks, Wildlife and Plant Conservation proposed that the government establish a number of forests as national parks. A lack of funds and competent personnel to successfully carry out this task meant those forests could only be declared as Forest Park. However, these were the ùseedsû of the national parks of today. In the meantime, legislation was proposed to conserve and protect nature and natural resources through the declaration of national parks. His Majesty the King gave royal assent by signing the National Park Act B.E. 2504 (1961) on 22nd September 1961.

According to the Act, a national park is defined as land, which includes mountains, creeks, swamps, canals, marshs, basins, waterways, lakes, islands and seashores which have been designated as national park areas. Those lands should include interesting scenery, and should not be private property legally owned by a person who is not a government entity. This is to keep such land in its original state, preserved for the education and recreation of the people.

On 18th September 1962, Khao Yai National Park was established as the first national park in Thailand, covering an area of 2,165.55 sq. km. in Nakhon Ratchasima, Prachin Buri, Nakhon Nayok and Saraburi provinces. From the time Khao Yai was established to the present. Currently, Thailand has a total of 147 national parks of which 127 parks have already been gazetted and 20 sites are in the process of being established, covering an area of 70,038.65 square kilometers or 13.64 percent of the total land

area of the country.