Parthamaspates, was the Roman client king of the Parthian Empire and later of Osroene. He was the son of the Parthian emperor Osroes I.
After spending much of his life in Roman exile, he accompanied the Roman Emperor Trajan on the latter's campaign to conquer Parthia. Trajan originally planned to annex Parthia as part of the Roman Empire, but ultimately decided instead to place Parthamaspates on his father's throne as a Roman client, doing so in 116. Following Roman withdrawal from the area, Osroes easily defeated Parthamaspates and reclaimed the Parthian throne.
After his defeat in Parthia, Parthamaspates again fled to the Romans who then, as a consolation, granted him the co-rule of Osroene, a small Roman client state between Asia Minor and Syria. He was king of Osroene together with Yalur from 118 to 122, and afterwards sole ruler to 123.