Primary tars produced from gas treatment in a low-temperature region were confirmed by thermogravimetric analysis of tar-mixed biomass that they would be easily handled by using simple reforming methods. A two-stage reactor was used to investigate the secondary reaction of light tar decomposition. The effect of air on light tar decomposition showed that gas products increased when the upper temperature was increased from 600 to 900 degrees C. When biomass char pyrolyzed to 900 degrees C was loaded in the upper reactor, the decomposition of light tar under inert atmosphere occurred by steam reforming to produce fuel gases even at a low temperature of 600 degrees C. When the upper temperature was increased to 800-900 degrees C, the yield of light tar significantly decreased and became almost zero because steam reforming and related reactions could proceed to produce CO and CO2 even in the case without biomass char. However, CO could be selectively obtained at the highest yield of 24.0 wt % because of the effect of catalytic char at a high temperature of 900 degrees C. Finally, alternative methods of light tar reforming are discussed for the development of a biomass gasification process to obtain tar-free gaseous products and/or valuable chemicals.