Catalytic steam reforming of tar derived from Japanese cedar pyrolysis was investigated over a prepared biomass char supported molybdenum carbide (Mo2C/BC) catalyst in a fixed-bed reactor. Mo2C/BC was prepared by in-situ solid state reaction, and characterized by XRD and SEM to study the effects of carburization temperature and Mo loading amount on Mo2C formation. The results show that Mo2C/BC catalyst was successfully prepared at a relatively low carburization temperature of 800 °C and the initial Mo loading amount for the preparation of this catalyst should be lower than 30 wt.%. The Mo2C/BC showed a good catalytic activity for the steam reforming of tar derived from biomass. In the case of Mo2C/BC with a Mo loading of 20 wt.%, the highest H2 yield was obtained, which is about 5 times higher than that of non-catalytic test. Mo2C/BC could be a promising catalyst in steam gasification of biomass to remove tar and produce H2-rich gas.