Gasification of woody biomass has been viewed as a promising technology for producing renewable energy and chemicals. However, product gas cleaning is still the bottleneck in advanced gas utilization. Laboratory scale experiments were conducted to investigate contaminant emission in product gas from an oxygen-steam blown updraft type gasification at the atmospheric pressure. Japanese cedar and willow were fed as feedstock at a feeding speed of 60 g/h and the concentrations of tar, hydrogen sulfide, carbonyl sulfide and hydrogen chloride in the product gases were measured varying feedstock, temperature, oxygen-fuel ratio, and steam-fuel ratio. Tar concentration and components were most affected by temperature. On the other hand other contaminants were highly dependent on feedstock.