In Greek mythology, Licymnius (/lɪˈsɪmniəs/; Greek: Λικύμνιος) was a good friend of Heracles' and an illegitimate son of Electryon, King of Tiryns and Mycenae in the Argolid (which makes him half-brother of Alcmene, mother of Heracles). His mother is given as Mideia, a Phrygian woman. One source mentions Alco (Ἀλκώ) as his sister.
Licymnius was the only one of Electryon's sons to return home after the unsuccessful war against the Taphians and Teleboans. Licymnius married Perimede, daughter of Alcaeus and sister of Amphitryon, and became the father of Melas, Argius and Oeonus. Licymnius accompanied Amphitryon when the latter was expelled from the Argolid and fled to Thebes.
According to one story, found in the Iliad, he was accidentally killed in his old age by Heracles' son Tlepolemus, when the latter was beating his servant with a stick and Licymnius ran in between (or else Tlepolemus and Licymnius had a quarrel over a certain matter). Pausanias mentions his tomb in Argos.