Prusias II Cynegus (c.182 - 149 BC) was the king of Bithynia. He succeeded his father Prusias I.

Prusias joined with Eumenes of Pergamon in a war against Pharnaces I of Pontus (181 - 179 BC). He later invaded the territories of Pergamon (156 - 154 BC), only to be defeated, and the Pergamenes insisted on heavy reparations. He sent his son Nicomedes II to Rome to ask their help in reducing the amount of these reparations, but Nicomedes revolted and became King.