Agios Ioannis Rentis (Greek: Άγιος Ιωάννης Ρέντης) is a suburb and a former municipality in the western part of the Athens-Piraeus agglomeration, Greece. Since the 2011 local government reform it is part of the municipality Nikaia-Agios Ioannis Rentis, of which it is a municipal unit.
Agios Ioannis Rentis is an industrialized suburb, located about 5 km (3 mi) west of central Athens and 3 km (2 mi) northeast of Piraeus. The small river Cephissus runs through it. Two important transport axes pass through the municipality: Motorway 1 (Athens- Thessaloniki) and the Piraeus–Platy railway, on which it has a passenger station (Rentis) and a large marshalling yard. The Olympiakos FC training center is in this area.