The acidic properties of Pd/ZSM-5 catalysts were characterized by NH3-TPD and FT-IR of d(3)-acetonitrile adsorption. Effect of Pd loading on the catalytic activity and product distribution was studied in the one-step synthesis of methyl isobutyl ketone from acetone. The results indicated that a proper balance between acidic and metallic sites was necessary to obtain high catalytic performance.