Sarn was a municipality in the district of Hinterrhein in the Swiss canton of Graubünden. On 1 January 2010 the municipalities of Portein , Präz , Sarn, and Tartar merged into the municipality of Cazis .

Sarn is first mentioned in 1156 as Sarn.

Sarn has an area, as of 2006, of 7.6 km2 (2.9 sq mi). Of this area, 78.9% is used for agricultural purposes, while 15.1% is forested. Of the rest of the land, 3.2% is settled (buildings or roads) and the remainder (2.8%) is non-productive (rivers, glaciers or mountains).