Alcetas I (Greek: Ἀλκέτας) (390/385 – 370 BC) was a king of Epirus.
Alcetas was expelled from his kingdom for unknown reasons, and took refuge with Dionysius I of Syracuse, who assisted him in being reinstated.
After Alcetas' restoration, he allied himself with the Athenians and with Jason of Pherae, the Tagus of Thessaly.
In 373 BC he appeared in Athens with Jason, for the purpose of defending the Athenian general Timotheus, who, through their influence, was acquitted.
Upon Alcetas' death, the kingdom was divided between his two sons, Neoptolemus I and Arybbas.