Composite membranes were prepared by the interfacial condensation of water-soluble diamines with an organic solvent (dichloromethane)-soluble dicarbomethoxy terephthaloyl chloride or carbomethoxy terephthaloyl chloride on top of a porous aluminum oxide support. The morphology of skin on the composite membranes is different in the two different procedures. The polyimide composite membranes with 40-times coatings provide a high gas permeation rate of oxygen and good permselectivity [alpha(O-2/N-2)]. The composite membrane with the polyimides skin at 40-times coatings had a gas permeation rate of oxygen range from 83 x 10(-5) to 130 x 10(-5) cm(3)(STP) s(-1) cm(-2) cmHg(-1), and a permselectivity [alpha(O-2/N-2)] range of 3.57 to 5.60. The composite membrane with poly(amide-imide)s skin at 40-times coatings had a gas permeation rate of oxygen range from 102 x 10(-5) to 146 x 10(-5) cm(3)(STP) s(-1) cm(-2) cmHg(-1), and the permselectivity (alpha(O-2/N-2)) range from 3.20 to 4.96.