Xenarchus was a Greek comic poet active in the 4th century BCE. He is identified as the son of Sophron, a famous writer of mimes from Syracuse in Sicily, and is sometimes called Xenarchus of Syracuse. According to the Byzantine encyclopedia, the Suda, he lived during the early part of the century. He worked during a period of transition in Greek comedy, between the older style of Aristophanes and the newer style of Menander.

Ancient sources attribute two comedies to him: The Pentathlete and The Scythian. Both plays are now lost, surviving only as titles, and no fragments are confidently assigned to them. It is possible he wrote other works that have not been recorded.

Xenarchus is a minor figure in the history of Greek comedy, and his significance lies primarily in his family connection. Modern scholars see him as a link between the influential Sicilian literary tradition of his father and the mainstream comic theater of Athens. Because his works do not survive, his personal style and contributions to comedy cannot be assessed.