St Mary's Church (Norwegian: Mariakirken i Oslo) was a medieval church in Oslo, Norway.
St Mary's Church, which functioned as royal chapel, had been built in stages with final additions made in the 1300s. The church was put 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.[1]