Various soluble polyimides with bis [4-(3-aminophenoxy)phenyl] sulfone and three kinds of dianhydrides were prepared in a polar N-methyl-2-pyrrolidone solvent by the traditional chemical two-step method. All the polymers synthesized had good solubilities in polar solvents and excellent thermal properties. Wide-angle X-ray diffraction studies showed that all polyimides were amorphous. Polyimide ultrafiltration asymmetric membranes were successfully prepared by the traditional phase-inversion method. The cross sections of the polyimide ultrafiltration membranes showed a very thin surface layer and a porous sublayer. The pure water flux was very high and the solute rejection rate at poly(ethylene glycol) of MW 20,000 was above 90%. (C) 2000 John Wiley & Sons, Inc.