Naissaar (; ) is an island northwest of Tallinn (but belonging to Viimsi Parish) in Estonia. It held a large Swedish minority until World War II, and during Soviet rule it was a military area and off-limits to the public.

A notable native of the island was Bernhard Schmidt, the Swedish-Estonian optician who invented the Schmidt telescope in 1930.

In December 1917, a group of Russian sailors commandeered Naissaar and proclaimed an independent "socialist republic" under the leadership of Stepan Petrichenko. The Russian sailors, numbering about 80-90, formed a self-styled government and levied taxes on the local population. The "republic" ceased to exist on February 26, 1918 when German forces occupied the island and the Russians fled.

Forty Bolshevik prisoners of war were executed by the Estonian Provisional Government here in February 1919.Jackson, Battle of the Baltic, page 9

See also

List of islands of Estonia