Rennes-en-Grenouilles () is a commune in the Mayenne department in north-western France.
The commune is made up of the following collection of villages and hamlets, Le Haut Hazay, Rennes-en-Grenouilles, La Guiberdière, Le Saussay, La Coquère, La Vieille Pellière and La Maillardière.
The Mayenne river flows through the commune.
The commune is located within the Normandie-Maine Regional Natural Park.