Abstract: A method for stripping U(VI) and an An(IV) from an organic solution including tri-n-butyl phosphate in an organic diluent, the solution containing U(VI) and the An(IV) present as U(VI) nitrate and An(IV) nitrate at concentrations such that the U(VI) nitrate concentration is higher than the An(IV) nitrate concentration, and the sum of the U(VI) nitrate and An(IV) nitrate concentrations is ?55 g/L. The method includes contacting the organic solution and an aqueous solution of nitric and oxalic acids, the oxalic acid concentration in the aqueous solution and the O/A volume ratio selected so that the oxalic acid is deficient with respect to the stoichiometric conditions of a complete precipitation of U(VI) and actinide(IV), to obtain a precipitate containing the actinide(IV) in oxalate form and a fraction of the U(VI) in oxalate form with a U(VI)/actinide(IV) mass ratio of between 0.5 and 5; and separating the precipitate from the organic and aqueous solutions.