The catalytic performance of Co/MgO catalysts (Co loading of 0-36wt%) for tar treatment in steam gasification of Radiata pine was investigated by means of the primary method using a fluidized bed reactor with Co/MgO catalyst as a fluidizing medium. Although the total amount of tar decreased with the presence of catalysts, water-insoluble components were found to increase while water-soluble components decreased. Among tested catalysts,]2wt% Co/MgO catalyst was found to exhibit the best catalytic performance (carbon-base total tar conv. 16%) with the smallest increase of water-insoluble components. The results of tar conversion for steam gasification of biomass sample were compared with those of cellulose gasification. The different tendency of tar conversion between cellulose and biomass was attributed to different phase of tar contacted with catalyst. It was concluded that the catalyst with larger surface area exhibited higher conversion for the tar derived from steam gasification of biomass. (c) 2007 Elsevier Ltd. All rights reserved.