In Greek mythology, Labdacus /ˈlæbdəkəs/ (Ancient Greek: Λάβδακος, Lábdakos) was the only son of Polydorus and a king of Thebes. Labdacus was a grandson of Thebes' founder, Cadmus. His mother was Nycteïs, daughter of Nycteus.

Polydorus died while Labdacus was a young child, leaving Nycteus as his regent, although Lycus soon replaced him in that office.^[1] When Labdacus had grown, he ruled Thebes for a short time. He died while he was still young, after he lost a war with the king of Athens, Pandion, over their borders.^[2] Apollodorus writes that he, like his cousin Pentheus, was ripped apart by women in a bacchic frenzy for disrespect to the god Dionysus.^[3] Lycus became regent once more after his death, this time for Labdacus' son, Laius. His descendants were called the Labdacids, and included his son Laius, who fathered Oedipus; Oedipus' children were Polynices, Eteocles, Antigone, and Ismene.