Rujan[1] (Serbian Cyrillic: Рујан) or Rujen (Рујен), is a mountain in southern Serbia, near the town of Bujanovac.

Its highest peak Kalje has an elevation of 968 meters (3,176 ft) above sea level.

On the mountain, there is Kale-Krševica archeological site, dating from the 13th century BC.

The Pčinja flows through the valley of Rujen.

This Serbia location article is a stub.