Polysulfone ultrafiltration membranes were prepared via the wet phase-inversion process with the same coagulation bath. Three different kinds of systems including polysulfone (PSF)/N, N-Dimethylacetamide (DMAC)/poly(vinyl pyrrolidone) (PVP), PSF/DMAC/Ethanol ternary systems and PSF/DMAC/Ethanol/PVP quaternary system were used as casting solutions. The zero shear viscosity of the casting solutions was measured and the phase-inversion process was monitored by the light transmittance apparatus. The surface and cross-section morphology of the corresponding membranes were characterized by SEM. The water flux and the anti-pressure stability of the membranes were performed in the permeation experiment. The pore size and porosity of the fresh and pressurized membranes were calculated. These experimental results suggest that the PSF ultrafiltration membrane of a density gradient structure prepared from the quaternary system by using PVP and ethanol together in PSF/DMAC/Ethanol/PVP solution with the respective amounts of 3.05 wt.%, 15.5 wt.%, has a good anti-pressure stability and a relatively high water flux (only changed from 162 L/m(2)h to 155 L/m(2)h) even by continuous operation (0.5 MPa) for 200 min, which is valuable as the sub-supporting membrane of composite membranes. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.