Saint-Denis-sur-Sarthon (French pronunciation: [sɛ̃ dəni syʁ saʁtɔ̃] ) is a commune in the Orne department in north-western France.

Notable Residents Saint Azélie-Marie ("Zélie") Guérin Martin mother of Saint Thérése of Liseux ( Saint Thérèse of the Child Jesus and the Holy Face)

The Commune along with another 11 communes shares part of a 5,255 hectare, Natura 2000 conservation area, called the Vallée du Sarthon et affluents.

• Large forge built in 1856 this blast furnace supplied Iron for the Alencon Railway, it was registered as a Monument historique in 1990.

• Communes of the Orne department
• Parc naturel régional Normandie-Maine