Electrochemical reduction of high dense UO2 pellets (95% TD) was carried out in molten CaCl2-48mol% NaCl at 923 K by constant voltage and constant current modes of electrolysis using graphite as the anode with an aim to check the feasibility of reduction and to determine the reduction mechanism. Electro-reduction experiments were carried out at 3.3 V for different durations of time (6, 12, 19, 25, 35 and 44 h) in order to obtain partially reduced samples. The UO2 pellets electrolysed for 35 h and above were fully reduced whereas those samples electrolysed for lower durations of time showed only surface reduction. Low current galvanostatic electrolysis of UO2 pellet showed gradual polarization of the cathode to higher cathodic values with time within a band of +0.250 V and 0.000 V vs (Na-Ca)/(Na+,Ca2+). No ternary intermediate compounds of the type Ca-U-O or Na-U-O or sub-oxides were observed in the partially reduced samples. Unlike in pure CaCl2 melt at 1173 K, the consumption of graphite anode and the carbon contamination of the melt were found to be minimum in the present study. Based on the experimental data, a probable mechanism of electrochemical reduction of UO2 to U in molten CaCl2-48mol% NaCl has been proposed. (C) 2013 The Electrochemical Society. All rights reserved.