Gasification of tar by catalytic steam reforming was examined in a circulating fluidized-bed (CFB) biomass gasification process. The tar reforming characteristics of the newly-developed Ni/MgO-CaO catalyst (based on dolomite), doped with WO3 as a sulfur-resistant promoter, was investigated using a simulated gas containing naphthalene as tar. Also, we applied this catalyst to the gasification of a biomass of dried sewage sludge and wood chips. The results of these basic experiments have confirmed that the newly-developed catalyst showed a high tar conversion activity, and is stable even in a gas containing hydrogen sulfide. The catalyst also exhibited superior resistance to coking as well as to sulfur poisoning, compared with several commercial steam reforming catalysts. The gasification demonstration plant (15 ton/d sewage sludge capacity) equipped with the present catalytic reformer showed almost complete tar conversion at 800-850 degrees C in the presence of 300 ppm sulfur.