Abstract: In a study for the development of the in-situ uranium and plutonium electro-reduction process and equipement, the dependence of U(VI)electro-re-duction rates on component concentrations has been investigated with the system UO2(NO3)2-HNO3-N2H5NO3(H2O)/30% TBP(OK). The electrolytic cell employed is a glass col.umn with an internal diameter of 50 mm. The sieve plates are made of titanium, serving as cathode, the anodical central rod is made of platinum or stainless steel, and the polyethylene material is used for the insulators between anode and cathode. The oscillation of reciprocating plate makes both phases dispersed.The U(IV) formation rates are measured under various component concentrations.The results show that the presence of hydrazine as the supporting reduc- tant or stabilizer is necessary for the reduction of U(VI). In the range of experimental concentrations, the U(VI) reduction rates are mainly dependent on the U(VI) concentration in the system and slightly dependent on the HNO3 and N2H6+ concentrations. The data for the present system are well correlated by the following rate equation:here the rate constant k is a function of temperature, k = 0. 00187 at t = 25℃.