Prusias I Chlorus (c.230 BC - 182 BC) was the king of Bithynia. The son of Ziaelas, he formed a marriage alliance with Philip V of Macedon.

Prusias fought a war against Byzantium (220 BC), then defeated the Gauls that Nicomedes I had invited across the Bosporus (218). He expanded the territories of Bithynia in a series of wars against Attalus I of Pergamum and Heraclea Pontica on the Black Sea. Philip V granted him the ports of Cius and Myrleia in 202, which he renamed Prusa and Apameia respectively.

Although he granted sanctuary to Hannibal, he remained neutral during Rome's war with Antiochus III the Great.

He was succeeded by his son Prusias II.