We have studied a high temperature steam gasification process to generate hydrogen-rich fuel gas from woody biomass. In this study, the performance of the gasification system which employs only high temperature steam exceeding 1200 K as the gasifying agent was evaluated in a 1.2 ton/day-scale demonstration plant. A numerical analysis was also carried out to analyze the experimental results. Both the steam temperature and the molar ratio of steam to carbon (SIC ratio) affected the reaction temperature which strongly affects the gasified gas composition. The H(2) fraction in the produced gas was 35-55 vol.% at the outlet of the gasifier. Under the experimental conditions, SIC ratio had a significant effect on the gas composition through the dominant reaction, water-gas shift reaction. The tar concentration in the produced gas from the high temperature steam gasification process was higher than that from the oxygen-blown gasification processes. The highest cold gas efficiency was 60.4%. However, the gross cold gas efficiency was 35%, which considers the heat supplied by high temperature steam. The ideal cold gas efficiency of the whole system with heat recovery processes was 71%. (C) 2009 Elsevier Ltd. All rights reserved.