Abstract: The kinetics of platinumcatalyzed reduction of U(Ⅵ) with hydrazine in perchloric acid media was studied. By investigating the influence of U(Ⅵ) concentration, hydrazine concentration, acidity and catalyst amounts (S/L) on the reaction, the reaction rate equation is obtained: -dc(UO²⁺₂)/dt=kc^0.39(UO²⁺₂)c^0.36(N₂H⁺₅)c^-0.51(H⁺), and the rate constant is 3.2×10^-3(mol/L)^0.76/min at 60℃ and the solid-to-liquid ratio of 0.002 kg/L. The effect of temperature was also investigated. The results show that while increasing the temperature, the reaction accelerates and the reaction process shifts from reaction-controlled to diffusion-controlled. Based on the above results, a possible reaction mechanism with the dissociation of adsorbed hydrazine on the catalyst as the the control step, is explored.