Preparation of polyimide composite membranes by the vapor deposition and polymerization method (VDP) has been investigated. 3,3’4,4’-Benzophenon tetracarboxylic dianhydride (BTDA), and 4,4’-diaminodiphenyl ether (ODA) were used as monomers. BTDA and ODA were simultaneously deposited on substrates in a vacuum of 10(-6) Torr, where the molar ratio of BTDA to ODA is unity. The deposition layer was converted from polyamide acid to polyimide by heating at 200 degrees C for 3 h in an ordinary vacuum oven. The substrates of the composite membranes used were polyimide asymmetric membranes. They were prepared by the phase inversion process from the casting solution of 24 wt% of commercial polyimide (PI-2080) and 76 wt% of N,N’-dimethylacetamide. The thickness of the deposited layer formed was ca. 0.05-0.4 mu m. Separation performance of polyimide composite membranes were measured by pervaporation method using a 95 vol% aqueous ethanol solution. A composite membrane with a deposition layer thicker than 0.2 mu m exhibited a separation factor of 1300.