Hydrogen production by gasification of biomass and waste organic compounds in supercritical water is a promising technology for utilization of wet organic compounds which cannot be used as a fuel because of its high moisture content. Catalytic as well as non-catalytic gasification has been investigated, and a high gasificaiton conversion was achieved Product gas is mainly composed of hydrogen, carbon dioxide, carbon monoxide, and methane. In order to obtain a high yield of hydrogen, methane generation should be repressed and water-gas shift reaction should be enhanced. Removal of carbon dioxide from hydrogen using only high-pressure water and utilization of nickel catalyst is also discussed.