A new procedure to prepare ultrathin membrane composed of nanoparticles was investigated. The nanoparticles were prepared in aqueous solution containing Pd-II ions by sonochemical reduction. Electrophoresis was used to fix the nanoparticles on a porous Substrate disc. The ultrathin membrane was successfully prepared with the combination procedure, and the obtained Pd membrane showed high perm-selectivity for H-2 and 3.85 of the separation factor of H-2/N-2 at room temperature.