The presented research results document deficient data on changes in the soil chemistry in middle altitudes. The research was carried out in the School Training Forest near Kostelec nad Cernymi lesy, 30 km SE of Prague, Czech Republic. Soil samples were taken from non-fertilized control plots (Luzulo-pilosse Abietum, Luzulo-Quercetum luzuletosum pilosae, Myrtillo-Abietum) in the altitude 400-450 m a.s.l., in 100-120 years old spruce monocultures. The first sampling took place in 1967, resampling in the years 2002/2003. As shown by our results, a considerable soil acidification occurred between the years 1967-2002/2003. The pH (KCl) decreased more than by 1 unit and the contents of the bivalent bases decreased in general. On the contrary, the contents of exchangeable Fe sesquioxides increased. Such results indicate soil degradation.