The praetorian prefecture of the East or of Oriens (Latin: praefectura praetorio Orientis, Greek: ἐπαρχότης/ὑπαρχία τῶν πραιτωρίων τῆς ἀνατολῆς) is one of four large praetorian prefectures into which the Late Roman Empire is divided after the death of Constantine the Great in 337, when the empire is split up among his sons and Constantius II receives the rule of the East, with a praetorian prefect as his chief aide.

The part allotted to Constantius encompasses four (later five) dioceses, each in turn comprising several provinces.

The authority of the prefecture stretches from the Eastern Balkans, grouped into the Diocese of Thrace, to Asia Minor, divided into the dioceses of Asiana and Pontus, and the Middle East, with the dioceses of Oriens and Egypt.As it comprises the larger part of the Eastern Roman Empire, and its seat is at Constantinople, the praetorian prefect is the second most powerful man in the East, after the Emperor, in essence serving as his first minister.