After successful synthesis and gas permeation study of ordered mesoporous nickelsilicate membranes on porous Al2O3 substrates, their catalytic properties have been evaluated in the reaction of styrene and benzene with H2O2. Nickelsilicate membranes have active properties for oxidation of styrene and benzene between 297 and 343 K. The effect of permeance of oxidant agent on the catalytic activity of membranes has been studied. Comparative experiments of the membrane reactor and batch reactor with the same catalyst (Ni-MCM-41) in power form revealed quite interesting observation that the oxidation of styrene with membrane reactor conducts to the formation of epoxy ethyl benzene (styrene oxide) while the conventional batch reactor with powdery catalyst gives selectively benzaldehyde. The activity and selectivity of nickelsilicate membrane catalysts have been correlated with their mesoporous structure, permeation properties and characteristics inherent to membrane reactor. It was found that the control of the oxygen peroxide feed and short residence and contact time of reactants and oxidant in membrane reactor result in the selectivity of styrene oxidation to styrene oxide instead of benzaldehyde, a deeper oxidation product, observed in batch reactor. The present paper supplies important information on designing highly efficient and selective catalytic membrane processes. (C) 2003 Elsevier B.V. All rights reserved.