Mosalsk (Моса́льск) is a town in Kaluga Oblast, Russia, located 82 km west of Kaluga (103 km by highway), the administrative centre of Mosalsky District. Population: 4,200 (2005 est.); 4,380 (2002 Census); 4,610 (1989 Census).
First attested in 1231 (recorded as Масальск, Masalsk), it became the centre of one of the Upper Principalities in the 14th century. After Ivan III annexed the principality to Muscovy in 1493, local princes emigrated either to Grand Duchy of Lithuania (where they became known as Princes Massalski) or to Moscow (where they were known as Princes Koltsov-Masalsky). Mosalsk was incorporated as a town of Kaluga guberniya in 1776. The town's main landmark is St. Nicholas Cathedral (1818, pictures).