Flavius Eustathius (Greek: Εύστάθιος, fl. 415–422) was a politician of the Eastern Roman Empire.
In 415-416 he was quaestor sacri palatii; in this capacity he received a copy of a law (Codex Theodosianus i.8.1, "De officio quaestoris", 15 October 415) he had promoted.
Between 420 and 422 he held the high office of Praetorian prefect of the East, while in 421 he held the consulate.