Časlav Klonimirović or Časlav of Serbia (c. 890s – 960) is Prince of the Serbs from c. 933 until his death in 960.

He significantly expands the Serbian Principality when he manages to unite several Slavic tribes, stretching his realm over the shores of the Adriatic Sea, the Sava river and the Morava valley.

He successfully fights off the Magyars, who have crossed the Carpathians and ravaged Central Europe, when they invade Bosnia.

Časlav is remembered, alongside his predecessor Vlastimir, as a founder of Serbia in the Middle Ages.

Časlav is the son of Klonimir, a son of Strojimir who rules as co-prince in 851–880.

He belongs to the first Serbian dynasty, the Vlastimirovićs (ruling since the early 7th century), and is the last known ruler of the family.