Sunday Lake (in French: lac Sunday) is a lake located in the municipality of Saints-Martyrs-Canadiens, in the Arthabaska Regional County Municipality, in the administrative region du Centre-du-Québec, in Québec, in Canada. It is headlake of the rivière au Pin, about 1.5 km (0.93 mi) upstream from Breeches Lake.

The lake, 2.5 km (1.6 mi) long and 600 metres (2,000 ft) wide, is private and the Brothers of the Sacred Heart own it; the banks are almost entirely wooded. Camp Beauséjour is a welcoming place for groups and families. Recreational trips, a family camp, and fishing are available.