Nam Khun (Thai: น้ำขุ่น, pronounced [náːm kʰùn]) is a district (amphoe) in the southwestern part of Ubon Ratchathani province, northeastern Thailand.

The government created the minor district (king amphoe) on 15 July 1996.

Neighboring districts are (from the west clockwise) Kantharalak of Sisaket province; Thung Si Udom, Det Udom and Nam Yuen of Ubon Ratchathani; and Preah Vihear of Cambodia.

The district is divided into four sub-districts (tambons), which are further subdivided into 49 villages (mubans).

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