Air-steam gasification of waste biomass was performed using a downdraft-fixed gasifier at atmospheric pressure and 1173K. The effect of a chemical property of waste biomass feedstock on the product distribution and product gas composition was statistically investigated. Twelve types of waste biomass and three types of model compounds of woody biomass were employed as feedstock. Gas, water soluble compound, water insoluble-acetone soluble compound, acetone insoluble compound, and char were obtained as products. Regardless of the variety of feedstock, the volatile matter content was the factor affecting the distribution to gas and product gas composition. The distribution to gas, i.e., the conversion to gas on a carbon basis, increased from 52.8 to 97.9C-mol% with an increase in the volatile matter content in the feedstock. The distributions to the water soluble compound, water insoluble-acetone soluble compound, and acetone insoluble compound were independent of the chemical property, and would be affected by the nitrogen and ash contents in the feedstock. The main product gas was H2 (20-35mol%), CO (15-30mol%), CO2 (20-35mol%), and CH4 (5-10mol%). When the volatile matter content was more than 70wt%, the molar ratio of H2 to CO in the product gas (H2/CO) decreased with an increase in the volatile matter content, while the molar ratio of H2 to CO2 (H2/CO2) was approximately unity and independent of the chemical property.In waste biomass with a volatile matter content of 70-80wt%, syngas with the desired H2/CO ratio for methanol synthesis was obtained. In waste biomass with a volatile matter content of more than 80wt%, syngas with the desired H2/CO ratio for dimethyl ether (DME) synthesis was obtained.