Demosthenes of Bithynia was a Hellenistic epic poet active in the 2nd century BCE. He is distinguished from the Athenian orator of the same name by his ethnic designation, which indicates his origin from Bithynia in northwestern Asia Minor. His floruit places him within the vibrant literary culture of the Hellenistic period.

Two epic poems are attributed to him, both now lost and known only through later references. The Bithyniaca concerned the history and mythology of Bithynia and is cited by the geographer Strabo. His second work was The Story of Troy, an epic on the Trojan War cycle.

Demosthenes is a minor but illustrative figure, representing the continuation and adaptation of the epic tradition to local histories and panhellenic myths in the Hellenistic era. The Bithyniaca is of particular note as a piece of local historiography in verse form, contributing to the literary expression of regional identity.