Pythagoreio is a former municipality on the island of Samos, North Aegean, Greece. Since the 2011 local government reform, it is part of the municipality Samos, of which it is a municipal unit. Population 9,003 (2001). It is the largest municipal unit in land area on Samos, at 164.662 km2 (63.576 sq mi). It shares the island with the municipal units of Vathy, Karlovasi, and Marathokampos.
The seat of the municipality was the town of Pythagoreio, formerly known as Tigani. The town was renamed in 1955 to honour the locally born mathematician and philosopher Pythagoras. The port of the town is considered to be the oldest man-made port of the Mediterranean Sea