Oannes may refer to:
- The enemy from Final Fantasy XIII-2.
- The boss from Final Fantasy XIV.
- The enemy from Final Fantasy Mystic Quest.
Oannes was the name given by the Babylonian writer Berossus in the 3rd century BCE to a mythical being who taught mankind wisdom. Berossus describes Oannes as having the body of a fish but underneath the figure of a man. He is described as dwelling in the Persian Gulf, and rising out of the waters in the daytime and furnishing mankind instruction in writing, the arts and the various sciences.