The paper describes transportation cost of the nuclear off-peak power for a hydrogen production based on water electrolysis in Japan. The power could be obtainable by substituting hydropower and/or fossil fueled power supplying peak and middle demands with nuclear power. The transportation cost of the off-peak power was evaluated to be 1.42 Y/kW h (1 US$ is equivalent to in about 115 Japanese)(at the end of 2005) when an electrolyser receives the off-peak power from a 6kV distribution wire. Marked reduction of the cost was caused by the increase of the capacity factor. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All fights reserved.