Agios Konstantinos is a village in Troizinia-Methana Municipality, in the regional unit of Islands, in the region of Attica, Greece. Agios Konstantinos lies at 13 m above sea level, at the foot of the Oneia mountains. It has 92 inhabitants (2021). The nearest city is Voula, 50 km to the northeast. Beaches nearby: Akti Agapis (3.1 km), Nisaki Beach (6.5 km), Russian Bay Beach (6.3 km). Among the landmarks around are Sanctuary of Asclepius (27 km), Ancient Theatre of Epidaurus (27 km) and Franchthi Cave (23 km). Among the natural features are Lazareto (10.0 km) and Soupia islet (15.9 km).

Also written Άγιος Κωνσταντίνος.