Metal oxides nanoparticles are of potential interest for pressure-driven membranes in view of flux increase and reduced fouling resistance. In this study, polyethersulfone (PES) flat-sheet membranes were manufactured by the phase inversion method for wastewater treatment application. A PES membrane was modified by dispersing nanoparticles of TiO2, Al2O3 and ZrO2 in a PES solution. Nanoparticles size distribution was characterized by scanning electron microscope (SEM) and dynamic light scattering (DLS) method to explore the effect of nanoparticle aggregation. Furthermore, membranes were characterized by hydrophilicity (contact angle), morphology (SEM), porosity, and thermal analysis (TGA). Membrane fouling was studied with BSA and humic acids as model organic foulants. Entrapped metal oxides changed the membrane morphology to more open and porous structure and the antifouling property and long term flux stability of metal oxide modified membranes were significantly enhanced. Strong correlations were observed between some physico-chemical properties such as, porosity, hydrophilicity and permeability of modified membranes with the spatial particle distribution in the membrane structure. The fouling resistance of modified membranes was significantly reduced, showing that the particle distribution is a key parameter for the membrane fouling reduction. The rejection potential of new membranes was hardly affected. (C) 2012 Elsevier B.V. All rights reserved.