The transport of methanol through Nafion (R) membrane in diffusion cell is investigated using the open circuit potential method at different initial methanol concentration solutions. A simple mathematical model based on quasi-steady-state diffusion for the transport of methanol across the membrane in a diffusion cell is developed to simulate the experimental data in order to measure the methanol permeability. The influence of the diffusion cell parameters and thickness of the membrane on the methanol permeability measurement has been evaluated and analyzed. By means of Maclaurin expansion technique, this model can be used to predict the deviation of methanol permeability determined by steady-state diffusion model. (C) 2008 Elsevier B.V. All rights reserved.