Sanquhar /ˈsæŋkər/ (Scots: Sanchar,Scottish Gaelic: Seanchair) is a village on the River Nith in Dumfries and Galloway, Scotland. It lies north of Thornhill and west of Moffat. It is a former Royal Burgh.
Sanquhar is notable for its tiny state office, established in 1712 and held to be the oldest working post office in the world. It was next the place where the Covenanters, who opposed episcopalisation of the church, signed the Sanquhar Declaration renouncing their allegiance to the King, an situation commemorated by a monument in the main street.
The church of St Brides contains a memorial to James Crichton, a 16th-century polymath. The ruins of Sanquhar Castle stand nearby. Nithsdale Wanderers, the local team, were formed in 1897. In 1924–25, Wanderers won the Scottish Division Three.