Mrázkův mlýn, Heritage mill building in Český Krumlov, Czech Republic.

Mrázkův mlýn is a historic mill situated along the Vltava River in Český Krumlov with traditional construction and a working water management system. The building displays the classic layout of a mill with preserved mechanical components and points where visitors can access the river.

The mill is first documented in 1347. Between 1613 and 1614 it was rebuilt in Renaissance style and converted into a paper mill. A dyer's house was added in the 18th century, the fulling mill was reconstructed in 1791–1798, and the dye works were rebuilt in 1869 and altered again in 1880. After the Kájov gates were demolished in 1881, a historicist house was built on the new street line.

The site preserves two separate workshops, a dye works and a fulling mill (valcha), installed here in the Renaissance period. The dye house was rebuilt in 1869 and altered again in 1880; before 1900 the fulling mill gained a second floor. A mill race led water from the weir to the wheel.

The mill stands in Kájovská street in the centre of Český Krumlov, on an island by the Vltava weir; the two protected buildings are Kájovská No. 56 and No. 58. The mill race that once fed the water wheel came from Mrázkův jez, the weir upstream, which has caused a number of fatal accidents among paddlers. Boaters should portage or scout it rather than run it.

The weir upstream, Mrázkův jez, has caused a number of fatal accidents among paddlers, so it is treated as a hazard on the Vltava. In 1930 the mill drove one Francis turbine with a flow of 2.85 m³/s, a head of 1.3 m and an output of 39 HP.