Japan has few indigenous energy supplies, and imports the bulk of its energy. so it is hardly surprising that, following the oil crises of the mid 1970＇s, it has taken renewable energy seriously. Moreover, increasing constrains on energy and the environment, especially the global environmental consequences of energy use, are causing a rising concern world wide, giving a warning that such constraints may be limits to sustaining our future development. This paper, at first, introduce prospects of energy demand and supply in Japan, then, the author look at the real potential of domestic renewable energy resources, such as solar thermal energy, photovoltaics, wind power, hydro power, ocean energy, biomass, and geothermal energy. Finally, the renewable energy strategy in Japan is asserted.