St Mary's Church, Oslo

Ruins, with shoreline visible. Modern skyline in the background.

Drawing of the church, based on a reconstruction

St Mary's Church (Norwegian: Mariakirken i Oslo) was a medieval church in Oslo, Norway. It was the royal chapel and had an important political role, as its provost from 1314 also was Chancellor of Norway.

St Mary's Church had been built in stages with final additions made in the 14th century. The church was set on fire by Swedish forces in connection with an attack in 1523. After the Reformation, it was so dilapidated that it could not be repaired and was demolished in 1542.

Excavations were first conducted in 1867 under Nicolay Nicolaysen and later in the 1960s under the leadership of Håkon Christie. Remains of two people, deemed to be King Haakon V and his Queen consort Euphemia of Rügen, were discovered during excavations of the ruins of the church and reinterred in the Royal Mausoleum in Akershus Castle. The church ruins are located in Middelalderparken near the neighborhood of Sørenga in the borough of Gamlebyen.