Mosterøy is an island in Stavanger municipality in Rogaland county, Norway.

The smaller islands of Sokn, Bru, and Åmøy lie to the south of Mosterøy and the islands of Klosterøy and Fjøløy lie to the west of Mosterøy.

All of these islands are connected together and to the mainland city of Stavanger by a series of undersea tunnels and bridges.

Both the tunnel and bridge are part of the European route E39 highway.

The highest point is the 154-metre (505 ft) tall mountain Mastravarden, located on the west side of Mosterøy.