The timber parish church was built in the 13th century, right after the town was founded. The current chancel and sacristy were built around 1337, and a small nave was added in the 15th century. The temple supposedly was founded by the king Casimir the Great. It was destroyed by a fire in the late 15th century and by the Swedish invasion in the mid-17th century. The church was renovated in 1721-1723, then it was restored in the 19th century, when the first porch was added to the nave. The second one was added in 1948.
The church is a brick building consisting of a short nave and a narrower chancel closed with polygon, covered with a rib vault. The nave was crowned only with a flat, wooden ceiling, although existing traces indicate the existence or planning of cross vaults. A barrel vault was established over the sacristy. A characteristic feature of the church is the curvature of the long axis of its nave in relation to the presbytery, probably resulting from its later building. The outer walls of the church were reinforced with three-step buttresses, between which tall and narrow pointed windows were pierced. The church has gable roofs and a mono-pitched over the sacristy. Inside are fragments of medieval frescoes from the end of the 14th century, preserved in the presbytery. There are paintings from the beginning of the 16th century in the nave.
Maluśkiewicz P., Gotyckie kościoły w Wielkopolsce, Poznań 2008.
Webpage zabytek.pl, Zespół kościoła par. pw. Wniebowzięcia NMP Ostrzeszów.