Oberste Stadtkirche St. Marien, Protestant church in Iserlohn, Germany.

Oberste Stadtkirche St. Marien is a church building in Iserlohn with two naves, a transept, and a mix of Gothic and Romanesque architectural details throughout its structure. The layout and design reflect how the building developed and changed over time.

A chapel dedicated to Cosmas and Damian, dependent on St. Pancratius, stood here and was probably built around 1330; the present Gothic church took shape in the 15th century, when the name Marienkirche came into use. The town fire of 1500 burned both west towers, which were rebuilt. After the Reformation the church became Iserlohn's main Protestant parish church.

The high altar's late-Gothic winged retable was carved by the Master of Iserlohn around 1455 and consists of eight panels depicting scenes from the life of Mary. It is considered one of the finest Flemish winged altars in Westphalia.

The church interior is entered from the west; the two tower halls there lead into the nave, with the sacristy on the south side of the choir and the irregular crypt beneath the choir. The 1972-1973 Karl Schuke organ has mechanical action and 42 registers on three manuals and pedal. Three cast-steel bells from the Bochumer Verein hang in the westwork, tuned to ais°-cis'-e'.

The high altar's late-Gothic hinged retable holds eight panels of the life of Mary, painted around 1455 by the Master of Iserlohn. Art historians count it among the finest Flemish winged altarpieces in Westphalia. The church also keeps a statue of Count Engelbert III of the Mark.