Holsnøy is an island in Alver Municipality in Vestland county, Norway.

The highest point on the island is the 324-metre (1,063 ft) tall Eldsfjellet, a mountain located about 2 kilometres (1.2 mi) north of the village of Rossland.

The island is hilly and marshy, with the majority of the residents living along the southern shore.

The island is connected to the mainland road network by a series of bridges.

The island of Flatøy is connected to Knarvik to the east on the mainland Lindås peninsula by the Hagelsund Bridge and Flatøy is also connected to Bergen to the south on the Åsane peninsula by the Nordhordland Bridge.