Pyro-processing is an electrochemical fuel processing technology for recycling the spent fuel into metal fuel for a nuclear fast reactor. The electrochemical processing for oxide fuel consist of electrochemical reduction, electro-refining, and electro-winning. In the electrochemical reduction process, most of uranium and transuranic elements can be reduced easily. However, the electrochemical reduction of rare-earth oxides is fairly difficult because of their thermodynamic stability and high oxygen affinity. It was already reported that the unreduced rare earth oxides react with UCl3 to form UOx in the electro-refining step, which causes serious problems in the electro-refining cell. In this study, co-reduction of rare earth oxides (Nd2O3, CeO2) and NiO has been investigated to increase the reduction degree of the rare earth oxides in the electrochemical reduction. The crystalline structure and morphology of the products were investigated by an X-ray diffraction (XRD) and a scanning electron microscopy(SEM), respectively. The products composition and reduction degree of rare earth oxide were estimated by an energy dispersive X-ray spectroscopy (EDS) and a thermogravimetric analyzer (TGA). CeO2-Nd2O3-NiO mixture was partially converted into NiNd2O4 during calcination, which can be easily reduced in the electrochemical reduction process. At the beginning of electrolysis, NiO in the mixed oxide started to be reduced into Ni metal in molten LiCl containing 1wt.% of Li2O. And then the reduction of the rare earth oxide (CeO2, Ce2O3, and Nd2O3) in the vicinity of the Ni metal took place to become the rare earth-Ni intermetallic compounds. The final products were identified to be RENi5-type intermetallics such as NdNi5 or CeNi5. According to EDS analysis, the oxygen contents of the reduced CeO2-Nd2O3-NiO mixture were found to be 4100 ppm. High reduction degrees of 99.23 and 98.80% were achieved with the Nd2O3-NiO and CeO2-NiO mixtures, respectively. The results demonstrate that co-reduction of rare earth oxides and NiO is an effective way to increase the reduction degree of rare earth oxides.