The Phaedra complex (/ˈfiːdrə, ˈfɛdrə/) is an informal, non-scientific designation to the sexual desire of a stepmother for her stepson, though the term has been extended to cover difficult relationships between stepparents and stepchildren in general.

The complex takes its name from Greek mythology. Phaedra was the daughter of Minos and Pasiphaë, wife of Theseus, sister of Ariadne, and the mother of Demophon of Athens and Acamas. Though married to Theseus, Phaedra fell in love with Hippolytus, Theseus' son born by either Hippolyta, queen of the Amazons, or Antiope, her sister.

When Hippolytus refused Phaedra's advances, she falsely accused him of propositioning her. Phaedra eventually killed herself in remorse after his subsequent death.