Institute for Transuranium Elements (ITU) is building up an accurate database of actinide behavior in chloride melts in support of its nuclear fuel reprocessing development program. The electrochemical properties of uranium, dissolved in LiCl-KCl eutectic melt, were investigated by transient electrochemical techniques, such as cyclic voltammetry (CV) and chronopotentiometry on an inert tungsten electrode. It was shown that U4+ is reduced to U-0 by a two-step mechanism corresponding to U4+/U3+ and U3+/U-0 transitions. In the 400-550° C (673-823 K) range, the diffusion coefficients of U3+ and U4+ were similar and equal to: D(U3+) = 13.7 x 10(-4) exph{-24.2 x 10(3)/RT(K)} and D(U4+) = 5.25 3 10(-4) exp{-19.8 x 10(3)/RT(K)} cm(2) s(-1). The apparent standard potentials of U4+/U3+ and U3+/U-0 redox systems were E-0* (U4+/ U3+) (V) = -1.902 + 0.0006104T (K) vs. Cl-2/Cl-and E-0* (U3(+)/U-0)(V) = -3.099 + 0.0007689T (K) vs. Cl-2/Cl-respectively. Some thermochemical properties (&UDelta; G*, γ) of uranium solutions were also derived from the electrochemical measurements. The Gibbs free energies of dilute solution of UCl3 and UCl4 in the LiCl-KCl were determined to be: &UDelta; G* = -897.09 + 0.226T (K) and -183.53 + 0.0589T (K) in kJ mol(-1), respectively. In the 400-550° C (673- 823 K) range, the activity coefficients γ of UCl3 and UCl4 range between 0.3-4.5 x 10(-3) and 17.1 -12.7 x 10(-3), respectively. © 2005 The Electrochemical Society. [DOI: 10.1149/ 1.1901083] All rights reserved.