Agios Konstantinos is a town in Oropos Municipality, in the regional unit of East Attica, in the region of Attica, Greece. Agios Konstantinos lies 7.8 km from the Parnitha mountains. It has 362 inhabitants (2021). The nearest city is Chalcis, 21 km to the northwest. Beaches nearby: Agios Konstantinos Beach (0.5 km), Akrotiri Beach (1.2 km), Saint Paraskevi Beach (2.1 km). Among the landmarks around are Parthenon (40 km), Amphiareion of Oropos (7.5 km) and Platonic Academy (38 km). Among the natural features are Mount Lycabettus (39 km) and Davelis Cave (30 km).

Also written Άγιος Κωνσταντίνος.