In the present study the catalytic steam gasification of biomass to produce hydrogen-rich gas with calcined dolomite and Nano-NiO/γ-Al2O3 as catalyst in an externally heated fixed bed reactor was investigated. The influence of the catalyst and reactor temperature on gasification performance was studied at the temperature range of 700°C-900°C. Over the ranges of experimental conditions examined, Nano-NiO/γ-Al2O3 and calcined dolomite both revealed better catalytic performance, at the presence of steam, tar was completely decomposed as temperature increases from 800°C to 900°C. Higher temperature resulted in more H2 and CO2 production, and dry gas yield. The highest H2 content of 58.27V% and the highest H2 yield of 2.23 Nm3/ kg biomass were observed at the highest temperature level of 900°C.