A new electrolytic deuterium separation system using a fuel cell has been proposed. It is found by calculation that the new system remarkably reduces energy consumption for heavy water production by reusing the hydrogen and oxygen gases at a fuel cell. However, the production cost is more expensive than that of the GS process which utilizes inexpensive heat energy. When voltage efficiencies of both the water electrolysis and the fuel cell exceed 87%, the new system will become a profitable process. (c) 2004 Published by Elsevier Ltd.