Ruotsalainen is a Finnish surname (literally meaning "a Swede", but as a name originally referring to the adherents of Lutheran Christianity in Karelia). It may refer to:
Ruotsalainen is a medium-sized lake of Finland in the Kymijoki main catchment area. it is located in Päijät-Häme, near the town Heinola. There is a waterway crossing the town and connecting the lake to another lake Konnivesi.