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Fifty-nine algal species were found on granite outcrops of the west-facing left bank of the river Pivdennyi Bug situated in the steppe area of Ukraine. Four sites were investigated: sites I (SW exposure) and II (NE) situated at the top of the river bank, and sites III (SW) and IV (NE) - at the bottom of a cliff. Species diversity of dry upper sites (I, II) was poor while in wet and dark lower sites (III, IV) it was more varied. The composition of assemblages of "actively growing" algal species of dry upper sites (I, II) depended on its exposition, while in wet and dark lower sites (III, IV) there was no such relationship. The composition of epilithic and chasmoendolithic algal groups was also different between sites according to light conditions. Growth of epiliths was suppressed in conditions of intense illumination (site I). Epiliths and chasmoendoliths are well developed in sites exposed to medium intensity of illumination (II, III). Chasmoendoliths are suppressed and epiliths are well developed in shaded site (site IV). Epilithic and chasmoendolithic communities had the same dominant species. The same dominant algal species were found on rock surface and in cracks in dependense of light conditions. Most of the diaspores found in air samples belonged to algae which form macroscopic growths on the surface of outcrops. Diaspore exchange between air and algae of granite cracks was more limited.