The addition of silica nanoparticles and poly(vinyl alcohol) (PVA) to polysulfone (PSF) membranes was used to modify the membrane morphology and enhance membrane performance. The central composite design of the response surface methodology was used to predict the maximum permeability and real salt rejection (R(real)) of the PSF membranes. The factors affecting the permeability and R(real) values of the PSF membranes were the silica (0-12 wt % PSF) and PVA (0-2 wt % PSF) contents. The optimized responses, membrane permeability, and R(real) obtained experimentally were 61.9260 L m(-2) h(-1) bar(-1) and 97.5850%, respectively, with deviation from the predicted values of 34.72 and 15.84%, respectively. In the further characterization, the contact angle results showed that PVA was important in stabilizing the nanoparticle surfaces to prevent agglomeration in the polymeric matrix. The tensile strength test confirmed that the addition of silica nanoparticles improved the mechanical strength of the PSF membranes. However, the addition of PVA had a weakening effect on the mechanical strength of the PSF membranes. The addition of silica nanoparticles and PVA affected the typical asymmetric structures of the PSF membrane less, as shown in the scanning electron micrographs. This may have been due to the good incorporation of additives in the PSF membranes, as observed from the energy-dispersive X-ray and Fourier transform infrared spectroscopy results. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 1804-1814, 2011