Membrane bioreactors (MBRs) have been widely used as advanced wastewater treatment processes in recent years. However, membrane fouling and its consequences in terms of plant maintenance and operating costs limit the widespread application of MBRs. Thus great efforts have focused on fouling mitigation. in this study, Al2O3 entrapped polyethersulfone (PES) ultrafiltration membranes were prepared and applied to activated sludge filtration in order to evaluate their fouling characteristics. The impact of solvent evaporation time and polymer concentrations on ultrafiltration (UF) membrane characteristics and performance was studied. PES was employed as a base polymer, while N-methyl pyrrolidone (NMP) was used as a solvent. The flat sheet membranes, prepared via phase inversion, were characterized using scanning electron microscope (SEM). Membrane performance was changed by the addition of Al2O3 nanoparticles to the casting solution. Al2O3 entrapped membrane showed lower flux decline compared to that of neat polymeric membrane. Fouling mitigation effect increased with nanoparticle content. No significant effect of the nanoparticles distribution pattern inside the membrane matrix was found on the membrane performance. This study highlights the potential of Al2O3 immobilized membranes in MBR application. (C) 2009 Elsevier B.V. All rights reserved.