Several multilayer thin-film composite membranes were fabricated of ethylcellulose (EC) and poly(aniline-co-ortho-toluidine) or poly(ortho-toluidine) blend as selective thin films and three ultrafiltration membranes with a 10- to 45-nm pore size and 100- to 200-mu m thickness as porous supports. The relationships between the actual air-separation performance through the composite membranes and layer number, composition, casting solution concentration of the thin selective film are discussed. The oxygen-enriched air (OEA) flux through the composite membranes increases steadily with increasing operational temperature and pressure. The oxygen concentration enriched by the composite membranes appears to decrease with operating temperature, but increases with operating pressure. The actual air-separation property through the composite membranes seems to remain nearly constant for at least 320 days. The respective highest OEA flux, oxygen flux, and oxygen concentration, respectively, were found to be 4.78 x 10(-5) cm(3) (STP)/s.cm(2), 2.2 x 10(-5) cm(3) (STP)/s.cm(2), and 46% across EC/poly(o-toluidine) (80/20) blend monolayer thin-film composite membranes in a single step at 20 degrees C and 650 kPa operating pressure. (C) 2000 John Wiley & Sons, Inc.