Abstract: Cationic ion exchange U(Ⅳ)-U(Ⅵ) redox displacement chromatography with citric, tartaric lactic, succinic,iminodiacetic acid and acetylacetone as complex agent was studied. The possibility and way to obtain high enrichment factor of uranium isotope separation as carboxylic acid is used as complex agent was mainly dealted. From the results it may be expected to increase the enrichment factor to (8.5-9.0)×10^-4, approaching the level offered by ion exchange process, if carboxylic acid is correct selected and its concentration as well as displacement ion concentration are properly controlled.