Saint Acacius was bishop of Melitene in the third century. The Greek Orthodox Church venerates him on different days, but especially on 31 March.

He lived in the time of the persecution of Decius, and although it is certain that he was cited before the tribunal of Marcian to give an account of his faith, it is not sure that he died for it. He was indeed condemned to death, but the Emperor released him from prison after he had undergone considerable suffering. He was famous both for the splendour of his doctrinal teaching and the miracles he wrought.

There was a younger Acacius, who was also Bishop of Melitene, and who was conspicuous in the Council of Ephesus, but it is not certain that he is ranked among the saints.