The study is focused on relationship between air pollution and species composition of epiphytic communities of bryophytes. Epiphytic bryophytes are good bioindicators (due to their characteristics), but bioindication ability of their communities was not sufficiently explored. Main aim of the study was to find out whether (and how) the structure of epiphytic communities on oaks (Quercus spp.) in the Czech Republic is affected by the air pollution. Additional aims should clarify whether the concentration of nitrogen in the moss thallus and the bark pH correspond with the level of air pollution, and whether the bark pH impacts species composition of epiphytic bryophyte communities. Bryophytes were studied on oaks across climatically similar but differently polluted areas in the Czech Republic. The data gained during the field research were completed with the map data and the chemical data – values of concentration of nitrogen in thalli of Hypnum cupressiforme Hedw. Structure of epiphytic bryophyte communities was significantly affected by the level of emission load. Clearly defined communities (belonging to vegetation order Orthotrichetalia Had. in Kl. et Had. 1944) were recorded on the study sites with low levels of air pollution. Communities from areas with higher levels of air pollution lacked any diagnostic species. Sensitive species of bryophytes, e. g. mosses from Orthotrichaceae family and liverwort Radula complanata (L.) Dumort., were more frequently recorded on less polluted study sites. Amount of nitrogen in thalli of Hypnum cupressiforme corresponded with level of NO2 pollution on particular study sites. Phorophyte bark pH was not directly affected by concentration of tracked pollutants in the air, but it influenced strongly epiphytic communities. Sensitive species of bryophytes preferred phorophytes with higher bark pH. According to results of this study communities of epiphytic bryophytes on oaks are significantly affected by air pollution. Only communities from areas with low level of air pollution are clearly defined and contain sensitive species. According to results of this study communities of epiphytic bryophytes have bioindication ability.