In this work, the high metal-dispersion Pd/Al2O3 composite membranes were prepared by wetness-impregnation technique. The effects of preparation parameters, including Pd precursor concentration, pH value and temperature, on the loading and particle size of Pd, and the characteristics of the resultant membranes were investigated. The experimental results showed that the impregnation of Pd followed the Langmuir-type adsorption model. The optimal conditions for impregnation were pH 1.5 and 1.2 wt.% Pd concentration. The size of Pd clusters estimated from the extended X-ray absorption fine structure spectroscopy (EXAFS) characterization was about 3.3 nm, independent of Pd loading within 2-7.8 wt.%. This revealed that the growth of Pd clusters was strongly hindered by the pore size of Al2O3 membranes. Furthermore, the blocking of Pd in pores resulted in the promotion of H-2/N-2 selectivity. (C) 2003 Elsevier Science B.V. All rights reserved.