Salsein (; ) is a commune in the Ariège department in the Pyrenees, in southwestern France.
It is located close to Castillon-en-Couserans, about 17 km south-west of Saint-Girons. It is part of the Ariège Pyrenees regional natural park.
The terrain is mountainous. The Bach, Cazalus and Coudères streams run through Salsein.
Inhabitants of Salsein are called Salseinois in French.