Mithridates I (c.195 BC - 138 BC) was the king of Parthia from 171 BC to 138 BC, succeeding his brother Phraates I. He was the son of Priapatius, King of Parthia (died 176 BC).
During his reign, the Parthians took Babylonia (144 BC), Media (141 BC) and Persia (139 BC). In 139 BC Mithridates captured Demetrius II of Syria, and Demetrius later married Mithridates's daughter Rhodogune.
His son Phraates suceeded him on his death as King.