Piraeus Prefecture (Greek: Νομός Πειραιά or Νομός Πειραιώς) was one of the prefectures of Greece.

As a part of the 2011 Kallikratis Programme, the prefecture was abolished, and its territory was divided into two regional units: Islands and Piraeus.

[1] The prefecture covered the south-western part of the agglomeration of Athens, several islands in the Saronic Gulf (Salamis, Aegina, Agkistri, Poros, Hydra, Dokos, Spetses, Spetsopoula), Methana and Troizina on the Peloponnese peninsula, and the islands of Kythira and Antikythera south of the Peloponnese.

An indication of the geographical diversity of the prefecture was the stark difference in population density between its seven mainland municipalities in the Athens urban area, which have 9,244.2 inhabitants/km2, and its detached outlying areas, which average only 85.83 inhabitants/km2 (and most of these on Salamis Island, at 395.40/km2, while the far-outlying parts have only 47.80/km2).

[citation needed] Note: Provinces no longer hold any legal status in Greece.