Agios Konstantinos is a town in Messene Municipality, in the regional unit of Messenia, in the region of Peloponnese, Greece. Agios Konstantinos lies 8.0 km from the Taygetus mountains. It has 78 inhabitants (2021). The nearest city is Kalamata, 10.8 km to the east. Beaches nearby: Oasi (1.5 km), Chelonaria (12 km), Kalamata (11 km). Among the landmarks around are Messene (3.5 km), Mystras (34 km) and Palace of Nestor (27 km). Among the natural features are Cave of Caiada (32 km).

Also written Άγιος Κωνσταντίνος.