The Korea Atomic Energy Research Institute is currently developing the Advanced Spent-Fuel Conditioning Process (ACP) based on a pyrochemical process. An electrochemical reduction process has been developed as a key unit of the ACP. In this work, an electrochemical reduction of U3O8 powder in a LiCl-Li2O molten salt has been investigated in an electrochemical cell with a unique cathode assembly, which consists of a porous magnesia membrane, oxide powder, and a solid electricity conductor. The experimental results suggest successful demonstration of this process, exhibiting a reduction conversion of U3O8 of >99% for a batch.