Petra () is a former municipality in Pieria regional unit, Greece. Since the 2011 local government reform it is part of the municipality Katerini, of which it is a municipal unit. The municipal unit has an area of 219.318 km<sup>2</sup>. The population was 4,225 in 2021. The seat of the municipality was in Mesaia Milia. Petra is also the name of a small settlement in the community Foteina, that had a population of 37 in 2011.