Phu Sing (Thai: ภูสิงห์, pronounced [pʰūː sǐŋ]) is a district (amphoe) in the southwestern part of Sisaket province, northeastern Thailand.

The minor district (king amphoe) was created on 1 April 1991, when the six tambons Khok Tan, Huai Ta Mon, Huai Tuekchu, Lalom, Takhian Ram, and Dong Rak were split off from Khunkhan district.

Neighboring districts are (from the west clockwise): Buachet of Surin province, Khukhan, and Khun Han of Sisaket Province, and Oddar Meancheay of Cambodia.

The district is divided into seven sub-districts (tambons), which are further subdivided into 85 villages (mubans).

There are no municipal (thesaban) areas, and seven tambon administrative organizations (TAO).