Abstract: The kinetics of U(Ⅵ) electro-reduction with the system of HNO3-N2H5NO3(H2O) /UO2(NO3)2-HN03 (30%TBP-OK) has been investigated. This is the first step of the investigation of the kinetics of U(Ⅵ) electro-reduction and reextraction. The experimental apparatus employed is a constant interfacial area cell (Lewis cell) with cathode and anode in it. The dependence of U(Ⅵ) electro-reduction rates on component concentrations in two phase solutions has been measured. According to the experimental data, a kinetics infinitesimal equation of U(Ⅵ) electro-reduction is given by.where k is rate constant, k= 1 .816×10-4 at t=25℃ The effect of the potential of cathode, the operating temperature, the stirring speed of two phases and the interfacial area between two phases on the U(Ⅵ) electro-reduction rates has also been investigated. The definition of the specific experimental conditions is introduced, the relation between the U(Ⅵ) electro-reduction rales and the specific experimental conditions is given by an empirical equation.where r0 is the U(Ⅵ) electro-reduction rate at the nominal experimental conditions. The process of U(Ⅵ) electro-reduction is mainly electrode reaction controlled.