The yields of the radiolytic oxidation of U-IV and of the U-VI formation, measured by spectrophotometry, are found to be the same (G(-U-IV)(N2O) = G(U-VI)(N2O) = 8.4 x 10(-7) mol J(-1)) and almost double the H-2 formation yield (G(H-2) = 4.4 x 10(-7) mol J(-1)) in the Co-60 gamma radiolysis of N2O-aqueous solutions ill the presence of 2 mol L-1 Cl- at pH = 0 (HCl). According to the mechanism of U-IV radiolytic oxidation, we show that under the conditions of our experiments the U-V ions do not disproportionate, but undergo a stoichiometric oxidation into U-VI by H+ with forming H-2.