The Diocese of Thrace is a diocese of the later Roman Empire, incorporating the provinces of the eastern Balkan Peninsula (comprising territories in modern southeastern Romania, central and eastern Bulgaria, and Greek and Turkish Thrace).

Philippopolis (modern Plovdiv, in Bulgaria) is the capital.The diocese is established as part of the reforms of Diocletian and Constantine the Great, and is headed by a vicarius subordinate to the praetorian prefecture of the East.

As outlined in the Notitia Dignitatum of ca.

400, the diocese includes the provinces of Europa, Thracia, Haemimontus, Rhodope, Moesia Inferior and Scythia.In May 535, with Novel 26, Justinian I abolishes the Diocese of Thrace.

Its vicarius retains his rank of vir spectabilis and receives the new title of praetor Justinianus, uniting in his hand both civil and military authority over the provinces of the former diocese, in a crucial departure from the strict separation of authority from the Diocletianian system.

A year later, in May 536, the two Danubian provinces, Moesia Inferior and Scythia, where detached to form, along with other provinces, the quaestura exercitus.