Thung Song is a district (amphoe) in the southwestern part of Nakhon Si Thammarat Province. Neighbouring districts are (from the west clockwise) Bang Khan, Thung Yai, Na Bon, Chang Klang, Lan Saka, Ron Phibun, Chulabhorn, and Cha-uat of Nakhon Si Thammarat Province; Huai Yot and Ratsada of Trang Province.