Kato Kastritsi (Greek: Κάτω Καστρίτσι) is a village and a community in the municipal unit of Rio, Achaea, Greece.

The community consists of the villages Kato Kastritsi and Magoula.

It is situated at about 100 m elevation in the northwestern foothills of the Panachaiko, 2 km southeast of Rio town centre, and adjacent to the campus of the University of Patras.

Ano Kastritsi is 4 km to the southeast.