In the Byzantine Empire, the Duchy of the Pentapolis is a duchy (Latin: ducatus), a territory ruled by a duke (dux) appointed by and under the authority of the Praetorian Prefect of Italy (554–584) and then the Exarch of Ravenna (584–751).

The Pentapolis (from the Greek term for "five cities") consists of the cities of Ancona, Fano, Pesaro, Rimini and Sinigaglia.

It lies along the Adriatic coast between the rivers Marecchia and Misco immediately south of the core territory of the exarchate ruled directly by the exarch (the Ravennate), east of the Duchy of Perugia, another Byzantine territory, and north of the Duchy of Spoleto, which is part of the Lombard Kingdom of Italy (founded in 568).

The duchy probably extends inland as far as the Apennine Mountains, perhaps beyond, and its southernmost town is Humana (Numera) on the northern bank of the Misco.

The capital of the Pentapolis is Rimini and the duke is both the civil and military authority in the duchy.