For persons with this surname, see Jacob Acontius and Melchior Acontius.

Acontius (Gr. Akontios), was in Greek mythology a beautiful youth of the island of Ceos, the hero of a love-story told by Callimachus in a poem now lost, which forms the subject of two of Ovid's Heroides (xx., xxi.).

During the festival of Artemis at Delos, Acontius saw Cydippe, a well-born Athenian maiden of whom he was enamoured, sitting in the temple of the goddess. He wrote on an apple the words, "I swear by the sacred shrine of the goddess that I will marry you," and threw it at her feet. She picked it up, and mechanically read the words aloud, which amounted to a solemn undertaking to carry them out. Unaware of this, she treated Acontius with contempt; but, although she was betrothed more than once, she always fell ill before the wedding took place. The Delphic oracle at last declared the cause of her illnesses to be the wrath of the offended goddess; whereupon her father consented to her marriage with Acontius (Aristaenetus , Epistolae, i. 10; Antoninus Liberalis, Metamorphoses, i., tells the story with different names).