Abstract: In the present work, hydrogen production from wood sawdust in supercritical water is investigated using a batch reactor. CaO was added to produce a clean gas free of environmentally unfriendly gases. The effects of CaO and reaction conditions on both yield and composition of the products are investigated. When Ca/C molar ratio is increased from 0 to 0.48, the yield of hydrogen increases from 3.2 mmol/g to 6.5 mmol/g. The results indicate that the key factor that affects the conversion of wood sawdust is the reaction temperature. The conversion of carbon to gas increases from 47% to 76% and the yield of hydrogen is increased from 4.5 mmol/g to 6.5 mmol/g with an increase of temperature from 773 K to 873 K. Compared with temperature, the influence of both residence time and pressure is less significant.