The Archar (Bulgarian: Арчар, pronounced [ɐrˈt͡ʃar]) or Archaritsa (Арчарица [ɐrˈt͡ʃarit͡sɐ]) is a river in the western Danubian Plain of northwestern Bulgaria and a right tributary of the Danube.

[1] The river takes its source at an altitude of 1,060 m, just 200 m east of the summit of Babin Zab (1,107 m) in the northwestern part of the Balkan Mountains.

The river then continues east through limestone terrain, forming a deep canyon-like valley with steep banks, in certain sections up to 100 metres high.

At the village of Ostrokaptsi the Archar bends to the northeast and at Vartop turns east.

[1] At its confluence with the Danube are situated the ruins of the important Roman town of Ratiaria.