Palladium membranes were prepared on an a-alumina support by metal-organic compound chemical vapor deposition (MOCVD) method from palladium(Ⅱ) acetate precursor. Permeation properties of hydrogen and helium gas were studied as a function of the number of times of deposition of palladium on the peeling off phenomenon of palladium, which is common in electroless plated membrane, was observed. Silica was introduced into the pores to prevent the palladium grain from peeling off. The palladium-silica conjugated membrane does not show the peeling off phenomenon and can withstand the high temperature up to 800CCCC which is the upper limit of our apparatus. The separation factor for hydrogen gas over carbon dioxide gas was improved with the increase of number of times of silica coating by sacrificing the H2 permeation and finally increased to four times. The improvement on the separation of hydrogen gas over carbon dioxide for palladium-silica conjugated membrane was evaluated and a model of permeation pattern Palladium membranes were prepared on an a-alumina support by metal-organic compound chemical vapor deposition (MOCVD) method from palladium (II) acetate precursor. Permeation properties of hydrogen and helium gas were studied as a function of the number of times of deposition of palladium on the peeling off phenomenon of palladium, which is common in electroless plated membrane, was observed. Silica was introduced into the pores to prevent the palladium grain from peeling off. The palladium-silica conjugated membrane does not show the peeling off phenomenon and can withstand the high temperature up to 800CCCC which is the upper limit of our apparatus. The separation factor for hydrogen gas over carbon dioxide gas was improved with the increase of number of times of silica coating by sacrificing the H2 permeation and finally increased to four times. The improvement on the separation of hydrogen gas over carbon dioxide for palladium-silica conjugated membrane was evaluated and a model of permeation pattern