The preparation and the pretreatment of Pd/ZnO catalysts were studied for methanol steam reforming. The presence of nitric acid in I'd nitrate precursor significantly altered the porosities and crystalline structures of the ZnO support. The dissolution of ZnO and extent of mixing between the Zn2+ and Pd2+ cations during catalyst preparation may have an impact on the PdZn alloy formation and its catalytic properties. The pretreatment of Pd/ZnO, which is critical to the PdZn alloy formation, depends not only on the reduction temperature but also on the reaction conditions under which hydrogen is formed. (C) 2003 Elsevier Science B.V. All rights reserved.