In this study, we examined oribatid fauna of strongly contaminated post-smelting dumps (southern Poland) that exist in the substrate and are associated with the most frequent lichen, Cladonia rei. Due to artificial origin of the substrate and the extremely high contamination with heavy metals, the studied dumps are unique in Europe in terms of unfavourable life conditions. In total, 2,936 specimens of Oribatida, representing 50 oribatid species, were sampled on 10 dumps and a reference site. Thalli of C. rei act as an island for soil oribatid mites on extremely contaminated post-smelting dumps. Both abundance and species richness of oribatid fauna collected from C. rei thalli were significantly greater than those recorded in the dump's substrate. The pool of oribatid species that was able to persist in extremely high doses of heavy metals was comparatively broad. However, only one species, Tectocepheus velatus, was able to achieve high abundances on all dumps. Three different responses of species (tolerant, sensitive, and indifferent) to heavy-metal contamination were recognised. Redundancy analysis indicated that highly increased levels of heavy metals, as well as K content, C/N ratio, and pH value, were the main factors that influence the composition and distribution of species. The concentrations of heavy metals (both essential elements (zinc) as well as xenobiotics (lead, cadmium) in T. velatus from the most contaminated dumps were not increased compared with those observed in moderately contaminated soils.