Sanquhar (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 post office, established in 1712 and held to be the oldest working post office in the world. It was also the place where the Covenanters, who opposed episcopalisation of the church, signed the Sanquhar Declaration renouncing their allegiance to the King, an event commemorated by a monument in the main street.