A research scale fluidized-bed reactor has been built and used to study the effect of steam/biomass ratio, time duration of experiments, reactor temperature, and biomass particle size on hydrogen yield and tar content in produced syngas during steam gasification of biomass. Batch experiments were performed with wood residue crushed into three different sizes of 0.5-1 mm (small), 1-2.5 mm (medium), and 2.5-5 mm (large), at reactor temperatures of 700, 800, and 900 degrees C. As the steam/biomass ratio increases, a decrease in formation of CO, accompanied by an increase in the hydrogen concentration, is observed. As expected, an increase in reactor temperature leads to a significant increase of H-2 output and tar reforming. The obtained results show that hydrogen yield increases as time duration of the experiment is increased. It is also found that a reduction in particle diameter leads to a significant improvement in hydrogen yield. (C) 2014 Elsevier Ltd. All rights reserved.