The Diocese of Dacia (Latin: Dioecesis Daciae) was a diocese of the later Roman Empire, in the area of modern western Bulgaria, central Serbia, Montenegro, Kosovo, northern Albania and northern North Macedonia.

Emperor Aurelian (270-275), confronted with the secession of Gallia and Hispania from the empire since 260, with the advance of the Sassanids in Asia, and the devastations that the Carpians and the Goths had created in Moesia and Illyria, abandoned the province of Dacia created by Trajan and withdrew his troops altogether, fixing the Roman frontier at the Danube.

A new Dacia Aureliana was organised south of the Danube out of central Moesia, with its capital at Serdica.

According to the Notitia dignitatum (an early 5th century imperial chancery document), the vicarius had the rank of vir spectabilis.

However, upon his death in 395, it reverted to the Eastern Empire, forming, together with the Diocese of Macedonia to the south, the Praetorian prefecture of Illyricum.