In this work, suction-assisted electroless deposition technique is proposed to prepare high hydrogen permselective Pd/Al2O3 composite membranes. Effects of suction pressure and plating time on the surface morphology and denseness of the resulting composite membranes have been investigated. Scanning electron microscopy (SEM), electron probe microscope analysis (EPMA), x-ray diffractometry (XRD), and nitrogen permeability technique were used to characterize these membranes. Furthermore, the hydrogen permeability and selectivity of the composite membranes were also studied. The experimental result shows that the nitrogen permeability of the palladium (Pd) top layer is decreased with lowering the suction pressure. Under suction pressure of 3 kPa and plating time of 1 hr, a membrane with a perfectly dense 4.5 mum thick Pd layer can be obtained, whose H-2/N-2 selectivity is approaching infinite. As compared to the conventional electroless deposition, via suction assistance, the adhesion between the Pd top layer and Al2O3 support of the resulting membranes can be remarkably improved, and the thickness attained for complete denseness can also be reduced effectively. Based on the hydrogen permeation results, it is found that the rate-limiting step for the hydrogen permeation through the Pd top layer is controlled by the surface reaction. Furthermore, the activation energy is estimated as 18 kJ/mol. This value is in a good agreement with those reported in literature for Pd layers thinner than 10 mum.