Pervaporation behaviors of water-2-propanol mixtures are examined using a polyethersulfone (PES) membrane and four kinds of sulfonated polyethersulfone (SPES) membranes with various contents of sulfonate groups. The fluxes of water and 2-propanol increase with increasing mole fraction of sulfonate group, s, in the membrane.Based on the solution-diffusion theory by considering water solubilities in the membranes, the fluxes of water and 2-propanol through these membranes were analyzed. There is no significant difference in the values of diffusion coefficients without swelling and the swelling parameters for water and 2-propanol among these membranes. It is found that the separation factors for various SPES membranes can be estimated from the parameter values for PES membrane by expressing the mole concentration in the membrane using the s value.