Khao Yai was Thailand's first national park, and was established on 18 September 1962. It is Thailand's third largest national park and covers 2,172 square kilometres taking in four provinces of the northeast. Much of the area is covered by virgin, old-growth tropical rainforest, but includes a wide variety of other habitats, including sub-montane evergreen and mixed deciduous forests and grasslands. There are also several mountains reaching heights of more than 1000 metres, but much of Khao Yai is sandstone plateau with elevations above 600 metres.

The national park is host to almost 2,500 plant species, 67 different kinds of mammals and over 300 species of birds. Tigers, elephants, gibbons, wild boars, Malaysian sun bears, and clouded leopards are just a few of the inhabitants of Khao Yai.

With its location high above sea level, Khao Yai is cooler and more pleasant than the hot, humid lowlands in Central Thailand. The dry season that lasts from November to February, when most people tend to visit, has temperatures that can fall as low as 4-6 º Celsius. The cool weather and the clear skies make this the favourite season for hiking and bird watching. The hot season is between March and April, followed by the May to October rainy season. The park is open during the rainy season, but hiking is more difficult, as raingear and leech medicine is necessary.

The entire area is criss-crossed by hiking trails, ranging in length from one and a half to eight kilometres and totalling to over 50 kilometres. There are in addition many waterfalls, the tallest and most spectacular of which is Haew Narok at 80 metres.