Mantsinsaari Island (also Mantsi, Russian: Остров Мантсинсаари, Finnish: Mantsinsaari) is an island on the northeastern edge of Lake Ladoga, in the Salmi settlement, Pitkyaranta, Karelia.

[1] Before World War II, when the island was a part of the Salmi municipality of Finland, it had around 1,500 inhabitants.

The main sources of livelihood were agriculture, cultivation and fishing.

During the Winter War, the artillery was utilised by Finnish troops in battles to the north of Lake Ladoga.

The Red Army was unable to conquer the island.