Nong Muang Khai (Thai: หนองม่วงไข่, pronounced [nɔ̌ːŋ mûa̯ŋ kʰàj]) is a district (amphoe) in the central part of Phrae province, northern Thailand.

The minor district (king amphoe) Nong Muang Khai was established on 1 April 1990 from tambons Mae Kham Mi and Nong Muang Khai of Rong Kwang district and Wang Luang and Nam Rat of Song district.

[2] Neighboring districts are (from the north clockwise): Song, Rong Kwang, Mueang Phrae, and Long.

The district is divided into six sub-districts (tambons), which are further subdivided into 34 villages (mubans).

Nong Muang Khai is a township (thesaban tambon) and covers most parts of tambon Nong Muang Khai.