Salmisaari (Swedish: Sundholmen) is a small area (a sector, pienalue) belonging to the Ruoholahti quarter of the Länsisatama neighbourhood of Helsinki, Finland.
The Salmisaari island was previously located west of the Helsinginniemi peninsula. However, during the early times of Länsisatama, it was annexed to the mainland by filling the sea in between. The area of Salmisaari has been named after this island.
Since 1953, Salmisaari has included the Salmisaari power plant, owned by Helsingin Energia. It also has offices of Altia (Salmisaarenranta 7). The opposite half of the same building acts as the Helsinki Court House.