The aim of this article is to show the course of castle-library auctions in the 1930s on the specific example of the Dietrichstein family. The sale of the Mikulov castle library is placed in the broader context of legal and social changes after the collapse of the Habsburg monarchy and the establishment of the First Czechoslovak Republic (the abolition of fideicommissum, a change in the status of the former nobility). and Kristýna Kaucká.