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

The 2.2-square-kilometre (0.85 sq mi) island lies in the district of Nordhordland, just north of the city of Bergen.

The northern part of the island, on the southwest shore of Kvernafjord, is very sparsely inhabited.

It lies between the Salhus neighborhood in the city of Bergen (to the south), the island of Holsnøy (to the west), and the village of Knarvik to the east.

[1] The island is the home to approximately 500 inhabitants, mostly in Krossneset, and was served by a local elementary school, Flatøy Skule until it closed in 2010.