This paper adopted three different techniques to characterize the membrane widely used in the studies of forward osmosis. The first technique involved estimating the pore size distribution of the membrane by modeling the rejection of simple uncharged solutes in hydraulic pressure-driven experiments. The pore size distribution was determined through the relationship between solute rejection and the Stokes radius of the neutral solute molecules. In the second method, the transmission electron microscopy was used to characterize the membrane. This method enabled the direct observation of open pore radius and directly confirmed the presence of discrete active and real physical pores. The third technique used to determine pore size distribution is the Brunauer-Emmett-Teller nitrogen adsorption. The results indicate that the forward osmosis membrane shows a significant distribution of pore size. The pore radius distribution is approximately skewed positively, and the mean value is 0.25-0.30 nm. This work also compared all the results, which show good agreement with the three techniques. Furthermore, the reflection coefficient is related to the pore size distribution obtained in this work, and the calculated values agree well with the experiment results. (C) 2013 Elsevier B.V. All rights reserved