Oxygen-blown co-gasification behavior in an entrained down-flow gasifier was investigated experimentally, using pulverized woody biomass and pulverized coal, at various mixing ratios, as the gasification fuel. The gasification temperature was controlled to over 1200 K and the oxygen ratio (O-2/O-2') was varied during the gasification experiments. The temperature of the gasifier and the composition and volume of the produced gas were measured; the carbon conversion, cold gas efficiency, and overall apparent reaction rates were calculated to evaluate the co-gasification behavior. The gasification temperature and composition of the produced gas varied significantly with the mixing ratio and oxygen ratio. The highest gasification temperature at the same oxygen ratio was observed for the fuel containing 20% woody biomass, due to enhanced oxidation reaction of the feedstock. The carbon conversion increased upon mixing woody biomass when compared to coal, due to the increased volatile content in the feedstock, but varied with the mixing ratio. The fuel ratio of the feedstock was identified as an important parameter for the cold gas efficiency and overall apparent reaction rate, which had a negative correlation with the fuel ratio when the oxygen ratio remained the same.