Uslar (German pronunciation: [ˈuslaːɐ̯] ⓘ; Eastphalian: Üsseler) is a town and a municipality in southern Lower Saxony, Germany, in the south-western part of the district of Northeim, and in the south of the hills of Solling forest which are part of the Weser Uplands.

Uslar lies close to the borders of Hesse and North Rhine-Westphalia.

The municipality of Uslar consists of 19 towns and villages: Ahlbershausen, Allershausen, Bollensen, Delliehausen, Dinkelhausen, Eschershausen, Fürstenhagen, Gierswalde, Kammerborn, Offensen, Schlarpe, Schönhagen, Schoningen, Sohlingen, Uslar, Vahle, Verliehausen, Volpriehausen and Wiensen.

Through Uslar passes the Bundesstraße (federal route) B241 out of direction of Beverungen to Northeim.

Uslar's industry uses the area's natural resources of wood, sand and water.