Brownfields are remnants of the functional and spatial transformations of urban areas in Poland. They are particularly abundant in old industrial districts, based on coal mining and metallurgy. The aim of this study is to identify the transformation directions and functional changes of brownfields in the former Upper Silesian Industrial Region in southern Poland, which has evolved into the Górnośląsko-Zagłębiowska Metropolis (GZM) through the process of socio-economic transformation. The study makes use of the χ2 test of independence and Cramer’s V as a post-test, and the method of in-depth interviews. The results indicate that the most popular new functions of post-industrial sites are production and services. When we consider large brownfields such as, in particular, disused mine dumps, dumping sites, settling ponds and workings, the most popular new form of land use is green spaces. Moreover, the study shows that the size of brownfields impacts their new forms of land use.