Recently, TiO2 nanoparticles blended within polymeric membranes have shown to provide improvements in fouling performance. However, agglomeration of nanoparticles remains as one of the major obstacles for generating a uniform surface, and also the mechanisms for improved fouling performance has yet to be elucidated. In this study, mechanical and chemical modification approaches were adapted using Degussa P25 TiO2 nanoparticles to improve their dispersion. Afterward, modified TiO2 nanoparticles were incorporated into polyethersulfone based in-house membranes and their effect on microstructure, surface chemistry, and fouling performance were investigated. Different techniques such as SEM, EDX, TGA, DSC, AFM, FTIR, contact angle goniometry, molecular weight cut-off, static protein absorption and surface free energy measurement were applied to characterize and explore the effect of different factors on fouling performance. The results showed that good dispersion of nanoparticles in the membrane was achieved after both chemical and mechanical modifications of particles, as a result of less agglomeration. The combination of chemical and mechanical modifications was found to have significant effects on surface free energy, roughness, surface pore size and protein absorption resistance as well as hydrophilicity. While previous researchers believe that the increase in hydrophilicity is the most likely reason for improvement in fouling performance, these other parameters such as changes in membrane morphology and local surface modifications may contribute just as much to greater fouling resistance when the effects of unmodified and modified titania were compared. (C) 2010 Elsevier B.V. All rights reserved.