Neighbouring provinces are (from north, clockwise) Chumphon, Nakhon Si Thammarat, Krabi, Phang Nga, Ranong.
Geographically, the centre of the province is the coastal plain of the Tapi River, mostly grassland interspersed with rubber tree and coconut plantations. In the west are limestone mountains of the Phuket range which are mostly covered with forest. Khao Sok National Park is there. To the east the hills of the Nakhon Si Thammarat (or Bantat) mountain range start to rise, protected in the Tai Rom Yen National Park.
Many islands in the Gulf of Thailand belong to the district, including the tourist islands Ko Samui, Ko Pha Ngan and Ko Tao, as well as the Ko Ang Thong Marine National Park.
The main rivers of Surat Thani Province are the Tapi River and the Phum Duang River, which join at the town Tha Kham shortly before they flow into Bandon Bay. The delta of these rivers, locally known as Nai Bang (ในบาง), is directly north of the city of Surat Thani. It consists of several channels with small islands mostly covered by mangroves and orchards.
Other protected areas in the province are the Khlong Phanom and Kaeng Krung National Park, Than Sadet-Ko Pha Ngan Marine National Park, the non-hunting areas Khao Tha Phet and Nong Thung Thong and the wildlife sanctuaries Khlong Phraya, Khlong Saeng, and Khlong Yan. The Hat Khanom - Mu Ko Thale Tai, which has a few small islands south of Ko Samui, is currently being created.