The paper deals with fluidized bed gasification of a biomass for producing a syngas with optimized hydrogen yield thanks to in-bed catalysis. Four different bed materials have been adopted: inert quartzite as reference case, olivine and dolomite as natural catalysts, and Ni-alumina as artificial catalyst. The gasification tests have been carried out at steady state in a pilot-scale bubbling fluidized bed, under operating conditions typical for gasification as reported in the paper. The gas analyses have been performed with dedicated instrumentation, like continuous analyzers and gas chromatograph, and adopting a standard protocol for tar sampling and characterization. The influence of the catalytic materials on the concentration of stable gases (e.g. H-2, CO2, CO, CH4 and light hydrocarbons) as well as on the efficiency of tar conversion has been studied. In particular the artificial catalyst has the largest effectiveness in enhancing the H-2 yield as well as in tar reduction. The catalyst gives rise to an elutriation rate significantly lower than that observed for dolomite at comparable U/U-mf ratio, denoting a better mechanical resistance. A stable activity of the nickel-alumina catalyst has been observed for the whole duration of reaction tests suggesting that no deactivation phenomena occurred, due to coke deposition or morphological modifications of the particles. (C) 2009 Elsevier B.V. All rights reserved.