Mithridates IV of Parthia ruled the western Parthian Empire from 129 to 140. He was the brother of Osroes I of Parthia (109–129). He was the youngest son of the Parthian King Vonones II. During the invasion of Mesopotamia by the Roman emperorTrajan (98–117) in 116 he and his son Sanatruces II took up the diadem but were defeated. After the death of Osroes I in 129 he assumed the throne and continued the struggle with the rival king Vologases III of Parthia (105–147). He died in an attack on Commagene in 140. Mithridates IV had appointed his son Sanatruces successor, but Sanatruces fell in a battle with the Romans. Another son, Vologases IV of Parthia (147–191), took the throne after the death of Vologases III in 147.