The Phetchabun mountains are a mountain range in Thailand. It extends in a roughly north-south direction, and separates the broad Chao Phraya river valley of central Thailand from the Khorat Plateau of northeast Thailand. The mountain range is named after the city of Phetchabun which is located in the mountains.

Until recently the mountains formed a barrier between the two parts of Thailand - only the railroad from Bangkok to Nakhon Ratchasima and one highway crossed it. Before the construction of the railroad in the beginning of the 20th century, the separation of the two parts of the country was even more distinct.

The highest elevation of the Phetchabun mountains is at 1820m above sea level at the Phu Hin Rong Kla National Park in the northern part of the mountain range. It consists of two parallel mountain chains, with the valley of the river Pa Sak in the middle. To the south the mountains end in the Khao Yai national park, and are continued to the east by the Dong-Paya-Yen, Sankambeng and Phnom-Dongrek mountain chains.

Geologically, the mountains consist of limestone, interfused with slate and sandstone. A few igneous rocks are also found: granite, basalt and porphyry.

Several national parks, forest parks and wildlife reserves are located in these mountains. In 2005 these were accepted by the UNESCO as a possible future addition to the World Heritage list. These sites include the Phu Hin Rong Kla National Park , Thung Salaeng Luang National Park , Phuluang Wildlife Reserve , Phukradung National Park , Nam Nao National Park , Phukhiew Wildlife Reserve and some forest reserves.