Agios Konstantinos is a town and former municipality in Phthiotida (Phthiotis), Greece. After the 2011 administrative division reforms it became part of the municipality of Kamena Vourla and it is now ranked as a municipal unit, with an area of 72.292 km2. Its population was 2,952 in 2021. The town has a harbor with a regular ferry-boat connection to the islands of Skiathos, Skopelos and Alonnisos. These islands are part of the Northern Sporades archipelago.