Diodorus of Sinope was a Greek comic playwright active during the 3rd century BCE, in the Hellenistic period. He was a practitioner of New Comedy, a popular style of theater that focused on domestic stories and recognizable character types rather than the political satire of earlier eras. According to ancient sources, he came from the city of Sinope on the Black Sea coast.

Only the titles of two plays attributed to him have survived: The Changeling and The Treasure. The plays themselves are completely lost, and no quotations or descriptions of their plots are known. He is not counted among the major surviving authors of his time, like Menander.

His historical significance lies primarily in being a documented example of the many comic poets from this fertile period whose works did not survive. His inclusion in later ancient catalogs shows he was remembered as part of the tradition, but with his writings lost, he remains a figure known only by name. According to modern scholars, he represents the vast majority of Hellenistic dramatists whose legacy exists only in such fragments of historical record.