Holy Cross Church (Norwegian: Korskirken) was a small medieval parish church for the northern part of the Old Town of Oslo, Norway. The ruin was rediscovered in 1922 and is now a part of the Ruin Park in Old Town (Ruinparken i Gamlebyen) containing the ruins of the church and the greater St. Hallvard's Cathedral.
There is no definite information about when the church was built. The church is not mentioned in the sources of the fighting in Oslo in 1240 between King Haakon IV and Duke Skule, suggesting that it is possibly younger. In 1989 a stick with runic inscriptions, dated to the first half of the 13th century, was found. The name Holy Cross Church occurs in these inscriptions, and it indicates that it may be older than 1240. When the church was built, it was located far north in the city, and an urban development north of the church came in the second half of the 13th century and the 14th century.
Holy Cross Church had input from the west, from the cemetery, an entrance from the west and an entrance directly to the chancel from the south. The remains of the original altar foundation is visible. Around the church are the remains of the cemetery wall.
Coordinates: 59°54′25″N 10°46′10″E / 59.90704°N 10.76948°E