Ni/alumina composite membranes were prepared and investigated for hydrogen separation at high temperature. cl-Alumina-supported gamma-alumina composite membranes were prepared by soaking-rolling method. In order to improve H-2 selectivity and permeance of the gamma-alumina membranes, Ni was deposited by a soaking process. As a result of a single gas permeation test of the Ni/alumina composite membranes, hydrogen permeance and H-2/N-2 selectivity at permeation temperature of 450 degrees C were 6.29 x 10(-7) mol/m(2) s Pa and 5.2 which exceeded theoretical Knudsen selectivity. Contribution of surface diffusion was investigated by temperature dependence of H-2 permeance. The surface diffusion was observed at higher temperature above 250 degrees C. The Ni deposition on surface of the gamma-alumina composite membrane led to hydrogen permeation via Knudsen diffusion combined with surface diffusion, which gave high H-2 selectivity exceeding the Knudsen diffusion mechanism. (C) 2007 Elsevier Inc. All rights reserved.