Philyllius was an Athenian comic poet active in the late fifth and early fourth centuries BCE. His career falls within the transitional phase between the Old Comedy of Aristophanes and the subsequent style known as Middle Comedy. The Suda records that he was victorious at the City Dionysia, though further biographical details are unknown.

His plays are now lost, surviving only in fragments and titles preserved by later authors. Known titles include Auge, Anteia, Cities, and Hellas, indicating comedies drawn from mythology as well as broader social or political themes. While the Suda attributes ten plays to him, only a handful of titles are now identifiable.

Philyllius holds significance for scholars tracing the evolution of Greek comedy. His work bridges the politically engaged and fantastical Old Comedy with the more generalized, character-oriented approach of Middle Comedy. The surviving fragments help illuminate how comic conventions, including mythological parody and social satire, developed during this critical fourth-century transition.