Montmerrei () is a commune in the Orne department in north-western France.
The commune is made up of the following collection of villages and hamlets, La Villette, La Grande Forgé and Montmerrei.
It is in size. The highest point in the commune is .
Montmerrei along with another 65 communes shares part of a 20,593 hectare, Natura 2000 conservation area, called the Haute vallée de l'Orne et affluents. In addition the commune along with another eight communes shares part of a 1,630 hectare, Natura 2000 conservation area, called Sites d'Ecouves.
The commune along with 26 others contains part of the Forêt d'ÃÂcouves.
The River Thouane, Landrion stream, Vallees stream and the Cercueil stream are the 4 watercourses that flow through the commune.