Koivusaari (Finnish: [ˈkoi̯ʋuˌsɑːri]; Swedish: Björkholmen; literally the "Birch Island") is an island and a part of the district of Lauttasaari in Helsinki, Finland. The island hosts two yacht clubs and a former Nokia training centre. The current island of Koivusaari has been formed by combining the island of Koivusaari proper with the island of Leppäsaari to the south of it and expanding it. Since the late 1990s and early 2000s there have been plans to construct a new residential area on reclaimed land in Koivusaari, served by the Koivusaari metro station.
Koivusaari is the westernmost district of the entire southern part of Helsinki. Directly west from it is a bridge across the Keilalahti bay, crossing the municipality border to Espoo, after which comes Keilaniemi, the easternmost district of southern Espoo.
Koivusaari metro station is a Helsinki Metro station since the Länsimetro extension 2017. It is Helsinki's westernmost metro station.