The zero shear viscosity of two kinds of polysulfone (PSF) casting solutions and the morphology and permeability of their membranes prepared via the phase-inversion process were investigated. The zero shear viscosities, dominated by changing the concentration of PSF and the molecular weight of poly(vinyl pyrrolidone) (PVP) additive for the PSF/N, N-Dimethylacetamide (DMAC) binary system and PSF/DMAC/PVP ternary system respectively, were measured by a falling sphere viscometer. The cloud point of solutions was investigated in the cloud point experiment, 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, and the water flux of the membranes was performed in the permeation experiment. Increasing the viscosity of the casting solution leads to the less porous surface and thick-skinned top-layer of the membrane. These experimental results are attributed to the mutable thermodynamic property of the system and the poor diffusion between components during the phase-inversion process, and finally results in the low water flux of PSF membranes. It suggests that the zero shear viscosity of the casting solution is one of the most important parameters for the morphology and permeability of membranes prepared via the phase-inversion process with the same coagulation bath. (C) 2010 Elsevier B.V. All rights reserved.