Khao Yai National Park is in the western part of the Sankamphaeng Mountain Range, at the southwestern boundary of the Khorat Plateau. The highest mountain in the area of the park is 1,351 metres (4,432 ft) high Khao Rom. This park lies largely in Nakhon Ratchasima Province (Khorat), but also includes parts of Saraburi, Prachinburi, and Nakhon Nayok Provinces.

The park is the third largest in Thailand. It covers an area of 300 square kilometers, including tropical seasonal forests and grasslands. Elevations mostly range from 400–1,000 metres (1,300–3,300 ft). There are 3,000 species of plants, 320 species of birds like red junglefowl and coral-billed ground cuckoo, and 66 species of mammals, including Asian black bear, Indian elephant, gaur, gibbon, Indian sambar deer, southern pig-tailed macaque, Indian muntjac, Ussuri dhole, and wild pig. There are no tigers in Khao Yai, and there have not been any for at least 20 years. Its waterfalls include the 80-metre (260 ft) Heo Narok, and Heo Suwat made famous from the film The Beach.

Recent wildlife studies show that animal ranges, particularly the few resident tigers, are impacted by human activity near the center of the park