Philyllius was an Athenian comic poet who lived and worked in the late 5th and early 4th centuries BCE. He belongs to the transitional period between Old Comedy, as practiced by Aristophanes, and the later style known as Middle Comedy. According to the ancient encyclopedia called the Suda, he was successful enough to win a victory at the major Dionysia festival, though the specific details of his life are not recorded.

His plays are now lost and survive only in fragments and titles mentioned by later writers. Known titles include Auge, Anteia, Cities, and Hellas, which suggest he wrote comedies based on mythology and broader social or political themes. The Suda credits him with writing ten plays, but only a few titles are known today.

Modern scholars consider Philyllius significant for understanding the evolution of Greek comedy. His career bridges two major styles: the politically charged, fantastical Old Comedy and the more generalized, character-driven Middle Comedy. The scant fragments of his work help academics reconstruct how comic themes, such as mythological parody and social satire, developed during this important 4th-century transition.