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 away from the coast of Finland, to the south-east from Hogland. The island is a part of the Leningrad Oblast, Russia. The area is approximately 8.3 km². There are no permanent inhabitants, save for a lighthouse keeper.
From the 16th century to 1939, it was populated by Finns. After the Soviet Union had attacked Finland in the Winter War, the island along with other Finnish islands in the Gulf of Finland and communities in Finnish Karelia had to be ceded to Soviet Union 1940. It was a lively Finnish fisher and trading community with population 436 (1939). Many cargo and fishing ships were registered to the island. It had a 1772 built wooden church, Finnish graveyard, school, 1904 built lighthouse, Finnish Coast Guard station and weather forecast station. Tourism was growing livelihood in 1920-39. Islanders were among the Finnish evacuees. After the war they were not permitted to return back to their homes like the rest of 422,000 Soviet evicted Finns. The name Tytärsaari means in Finnish - "Daughter Island" .
Bolshoi Tyuters has been known as the "mined island" because its minefields have not been cleared since World War II.