Bolshoi Tyuters (Russian: Большой Тютерс; Finnish: Tytärsaari; Estonian: Suur Tütarsaar; Swedish: Tyterskär) is an island in the Gulf of Finland of the Baltic Sea, located 75 km (47 mi) away from the coast of Finland, to the south-east from Hogland.

After the Soviet Union attacked Finland in the Winter War, the island, along with other Finnish islands in the Gulf of Finland and communities in Finnish Karelia, was ceded to the Soviet Union under the Moscow Peace Treaty of 1940.

Islanders were among the Finnish evacuees, and after World War II they were not permitted to return to their homes.

Bolshoi Tyuters is sometimes referred to as the "mined island" because its World War II minefields have not been cleared.

Thousands of rusting pieces of German equipment and weaponry, including artillery and ammunition, are scattered on the island.