Mariä Himmelfahrt, Parish church and architectural heritage monument in Grassau, Germany.

Mariä Himmelfahrt is a Gothic-origin, Baroque hall church in Grassau. Its square west tower, built to roof height in the early 13th century, has Romanesque triple arcades and a Baroque onion dome. The nave, rebuilt from 1476 as a three-aisled hall, is covered by a net vault whose ribs were removed in 1706 and replaced with stucco by Giulio Zuccalli. The choir has a three-sided close and a south sacristy.

The church is documented over 1000 years ago; the tower was built to roof height in the early 13th century, and the choir and nave walls date from the 14th century. From 1476 the nave was rebuilt as a three-aisled hall church, with the year 1491 above the west portal. After lightning destroyed the roof in 1570, the present roof structure was dated 1572–1574. Baroque work followed in three phases: 1639–1642, 1672–1685 and 1695–1707.

The church's name refers to the Assumption of Mary, and its fresco cycle centres on Mary and the Scapular Brotherhood founded in 1700. Under the organ gallery, a surviving 1707 painting by Jacob Carnutsch of Prien shows the procession of Grassau's three brotherhoods. The pulpit, added in 1654, carries figures of the Evangelists and musical putti on its canopy.

The church stands on the Grassauer Kirchplatz, a square that once served as a court site. The west tower with its onion dome marks the main axis; the two chapels on the south side are joined into a single side-aisle-like room. The interior is entered from the west, and the raised nave is reached over round pillars.

Under the gallery vault, a 1707 fresco by Jacob Carnutsch of Prien survives, showing the procession of Grassau's three brotherhoods; it is the only part of his cycle not painted over in 1766/1767 by Johann Nepomuk della Croce. On the north wall hangs a rare motif: the parish priest Matthias Winkler on his deathbed, painted after 1715.