Tan Sum (Thai: ตาลสุม, pronounced [tāːn sǔm]) is a district (amphoe) in the central part of Ubon Ratchathani province, northeastern Thailand.

The minor district (king amphoe) Tan Sum was created on 18 September 1978, when the three tambons Tan Sum, Samrong, and Chik Thoeng were split off from Phibun Mangsahan district.

[2] The old name of the area was Tan Chum (ตาลชุม), which means fertile land with plenty by Toddy palm trees (Borassus flabellifer).

Neighboring districts are (from the east clockwise) Si Mueang Mai, Phibun Mangsahan, Sawang Wirawong, Don Mot Daeng, and Trakan Phuet Phon of Ubon Ratchathani Province.

The district is divided into six sub-districts (tambons), which are further subdivided into 59 villages (mubans).