Karlsøya or Karlsøy () may refer to:
Places Norway Karlsøy Municipality, a municipality in Troms county Karlsøy Church, a church in Karlsøy Municipality in Troms county Karlsøy, Nordland, a village in Hamarøy municipality in Nordland county Karlsøya (Møre og Romsdal), an island in Molde municipality, Møre og Romsdal county Karlsøya (Nærøysund), an island in Nærøysund municipality, Trøndelag county Karlsøya (Nordland), an island in Bodø municipality, Nordland county Karlsøya (Ørland), an island in Ørland municipality, Trøndelag county Karlsøya (Troms), an island in Karlsøy municipality, Troms county Karlsøya (Østfold), an island in Sarpsborg municipality, Østfold county