The electrochemical behavior of UCl4 and UCl3 in LiCl-KCl eutectic melt was studied at 723- 823 K by different electrochemical methods. Electroreduction of U(IV) in LiCl-KCl melt occurs via two successive steps involving transfer of one and three electrons. The diffusion coefficients of U(IV) and U(III) were determined by linear sweep voltammetry, chronopotentiometry, and chronoamperometry. The values found by these methods are in a good agreement with each other. The standard rate constants for the redox reaction U(IV) + e(-) -> U(III) were calculated from cyclic voltammetry data and for the discharge process U(III) + 3e(-) U by using the impedance spectroscopy method. The values of constants testify that the redox process proceeds quasireversibly, mostly under diffusion control, while electrodeposition is mainly controlled by the rate of charge transfer. The formal standard potentials of E*(U(IV)/U(III)), E*(U(IV)/U), and E*(U(III)/U) * were determined by different electrochemical methods and some thermodynamic properties of UCl4 and UCl3 dissolved in a LiCl-KCl eutectic melt were calculated. The influence of oxide ions on the electrochemical behavior of the LiCl-KCl-UCl4 melt was studied. (c) 2005 The Electrochemical Society. All rights reserved.