Uranium mineralization is present in organic rich grey arkosic sandstones in the Permian strata of the Kozie Chrbty Mts. in the Western Carpathians. Dominant ore minerals are uraninite, pyrite, chalcopyrite, tennantite, galena and sphalerite. The organic matter was analysed by microphotometry, Rock-Eval pyrolysis and gas chromatography. The organic matter is of humic type at a stage of thermal maturity corresponding to medium volatile bituminous coal. Uraninite formed from solutions that evidently infiltrated the tissues of terrestrial plants at a very early diagenetic stage. Organic matter acted both as a sorbent and a reducing agent. The bands of uraninite grains in vitrinite are cut by younger quartz-dolomite-sulfide veinlets. The temperature to which the rocks were exposed during deepest burial is estimated at 100–150°C.