Southern Thailand is located on the Malay Peninsula, with an area around 70,713 km², bounded to the north by Kra Isthmus as the narrowest part of the peninsula. The western part has steeper coasts, while on the east side river plains dominate. The largest river of the south is the Tapi in Surat Thani, which together with the Phum Duang in Surat Thani drains more than 8,000 km², more than 10% of the total area of Southern Thailand. Smaller rivers include the Pattani, Saiburi, Krabi and the Trang. The biggest lake of the south is the Songkhla lake (1,040 km² altogether), the largest artificial lake is the Chiao Lan (Ratchaprapha dam) with 165 km² within the Khao Sok national park in Surat Thani. Surat Thani Ko Lao Liang Phi with the steep limestone hills present at most of the western coast.
Running through the middle of the peninsula are several mountain chains, with the highest elevation at the 1835 m high Khao Luang in the Nakhon Si Thammarat Province. Ranging from the Kra Isthmus till the Phuket island is the Phuket chain, which connects to the Tanao Si Mountain Range further north. Almost parallel to the Phuket chain but 100 km to the east is the Nakhon Si Thammarat or Banthat chain, which begins with the Samui island Ko Pha Ngan Ko Tao in Surat Thani and ends at the Malaysian border at the Ko Ta Ru Tao archipelago. The border to Malaysia is formed by the Sankalakhiri range, sometimes subdivided into the Pattani, Taluban and Songkhla chain. At the border to Malaysia begins the Titiwangsa chain.
The limestone of the western coast has been eroded into many steep singular hills. Those parts submerged by the rising sea after the last ice age now form the many islands, like the well known Phi Phi Islands. Also quite famous is the so-called James Bond Island in the Phang Nga Bay, which featured in the movie The Man with the Golden Gun.