Koivusaari (Swedish: Björkholmen) is an island and a district of Helsinki, Finland.
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 will have its own metro station when the Länsimetro extension is implemented, most probably in early 2013. It will then become Helsinki's westernmost metro station.