Prusias I Chlorus (ca. 228 BC – 182 BC) was a 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. 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 Keios and Myrleia in 202, which he renamed Prusias and Apameia respectively.

Although he granted sanctuary to Hannibal, who fought aganist the Attalids for him, he remained neutral during the Roman Republic's war with Antiochus III the Great.

He was succeeded by his son Prusias II.

---- Habicht, Christian, s.v. Prusias I., RE. Bd. ХХШ, 1. 1957 ----