In this paper, ternary phase diagram was used to predict morphology of the membranes prepared via phase inversion process. Theoretical ternary phase diagrams were calculated based on a compressible regular solution (CRS) model for water/dimethylsulfoxide/polyethersulfone membrane forming system. The CRS model is an alternative for the traditional Flory-Huggins theory. The experimental cloud point data were determined using titration method. The constructed theoretical ternary phase diagrams were consistent with the experimental results. The precipitation rate of the polymeric solution in the nonsolvent was obtained by light transmission experiments. The membrane morphology was predicted using the theoretical phase diagram and the phase separation kinetics. To verify this prediction, the light scattering experiments were performed. (C) 2012 Elsevier Ltd. All rights reserved.