The Sainte-Marguerite River Old Forest (French: Forêt ancienne de la Rivière-Sainte-Marguerite) is a protected area of old-growth forest in the Saguenay–Lac-Saint-Jean and Côte-Nord regions of Quebec, Canada.It is classified as an exceptional forest ecosystem. It protects an area on the northeast bank of the Sainte-Marguerite River.