Polysulfone (PSI) membranes are undesirably hydrophobic, thus they are susceptible to the fouling by most organic components including fatty acids. In this work. ZnO nanoparticles were blended into PSf membranes to improve its properties in reduction of fouling by oleic acid. The casting solution was prepared by dispersing 1-4 wt.% of ZnO nanoparticles (21-23 nm), 1 wt.% of PVA and PSf into 1-methyl-2-pyrrolidinone at 75 degrees C, with a stirring speed of 400 rpm. The weight ratio of polymer to solvent is maintained at 1:4.84. The composite membranes were then prepared using phase inversion method. The mean pore size of the composite membranes is slightly larger than the mean pore size of pure PSf membrane. However, the water contact angle greatly reduces from 85 degrees to 63 degrees when 2 wt.% of ZnO is added into Pf-2 membranes. Thermal stability of PSf membranes has significantly improved with the addition of ZnO. Although absorption peaks of ZnO are absent in FT-IR patterns, EDX analysis shows that ZnO nanoparticles are well distributed in the dense layer of Pf-2 membrane. Hence, Pf-2 membranes show the highest permeability and the least fouling by oleic acid. (C) 2012 Elsevier B.V. All rights reserved.