Tamasio () is a former municipality in the Karditsa regional unit, Thessaly, Greece. Since the 2011 local government reform it is part of the municipality Sofades, of which it is a municipal unit. The municipal unit has an area of 163.504 km<sup>2</sup>. Population 2,421 (2021). The seat of the municipality was in Leontari. The municipality was named after Mount Tamassion (Tamasion was also the old name of the village of Anavra).