Feldschlösschen, Industrial brewery in Rheinfelden, Switzerland.

Feldschlösschen is a brewery complex in Rheinfelden whose red brick and pale yellow buildings stand on a grassy slope. A tall square tower with a clock face and flagpole rises beside a multi-storey block with pale-framed windows and an arched entrance; a lower range carries the name "FELDSCHLÖSSCHEN" on its facade. The castle-style factory buildings were erected from the 1880s to the 1910s and are protected as a monument.

The brewery was founded in 1876 by brewer Theophil Roniger and farmer Mathias Wüthrich on the site of a disused aniline factory south of Rheinfelden station, and Roniger began brewing there on 8 February 1876. Converted into a joint-stock company in 1890, it bought up and closed 27 Swiss breweries by 1930 and became the country's largest beer producer in 1898. Carlsberg took over the beverages business in 2000.

The name Feldschlösschen, "small castle of the field", comes from the castle-style factory buildings put up between the 1880s and 1910s, planned by the Frankfurt firm Langeloth and Zimmermann of Freiburg. The complex is a listed monument. The brewery can be visited, and the water for brewing comes from a spring near Magden.

The brewery in Rheinfelden can be visited on guided tours; the water for brewing comes from a spring near the neighbouring village of Magden. The A3 motorway runs directly south of the factory buildings, and the Rheinfelden Ost exit is about one kilometre east, linked to the site by Theophil-Roniger-Strasse. The Bözberg railway line passes on the north side.

The castle-style factory buildings were put up between the 1880s and 1910s, planned by the Frankfurt office Langeloth and the Freiburg office Zimmermann, drawing on several architectural periods. The complex is listed as a heritage site, and the brewery's own railway station, built around 1900 beside the Bözberg line, served the site.