In this paper, the flux and separation factor for water/ethanol mixtures in PVA membrane system are detected and a modified solution-diffusion model is proposed to account for the mass transport of penetrants in the polymer membrane. In the model, the group contribution method (the UNIFAC-ZM model) is introduced to calculate the activity of penetrants in the polymer membrane, and a modified Fujita temperature-dependence diffusion coefficient equation is developed to describe the diffusion behavior of the penetrants. The aim of this work is to establish a predictive solution-diffusion model. As an exemplary application of the model, the permeation fluxes and separation factors of water/ethanol mixtures in PVA membrane system have been predicted and showed to be in good agreement with experimental values. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.