The235U/238U isotope fractionation occuring in cation exchange chromatography of a system U(IV) –citric acid containing sulfuric acid was investigated at various temperatures. A clear displacement chromatogram was obtained at only a limited composition and pH of the eluent. It was found that235U is depleted at the front of the uranium band, and enriched at the rear. This result was opposite to that observed in the U(VI) complexation systems. The235U/238U single stage separation coefficient ɛ (defined by Eq. (4)) decreased with rising temperature.