The Chateau’s chapel was built in the second half of the 18th century. A convex crown connects its interior with the frescoes of the Assumption of the Virgin and the figures of evangelists. In frames, among ornamental mural paintings, are frescoes of saints by the Italian painter G. Doverio. The main altar, in baroque style with Venetian mirrors and the coat of arms of Count Salm of Štemberk who owned Štiřín from 1751 to 1797, dates back to 1775.

The altar is dominated by the Palladium of the Virgin Mary of Stará Boleslav

Small side rococo pilaster altars with the paintings of Nativity and St. John of Nepomuk. Smaller paintings depicting St.Tekla and St. Peregrine. Wooden benches dating back to 1896.

Today, the Chapel is used for concerts of live and reproduced music and wedding ceremonies.