A polyvinylidene fluoride (PVDF) ultrafiltration (UF) membrane was modified by dispersing nano-sized alumina (Al2O3) particles uniformly in a PVDF solution (19% polymer weight). Membranes were prepared by a phase-inversion process and using UF experiments comparing water flux and, molecular-weight cut-offs for the wet membranes. The contact angle between water and the membrane surface was measured in order to quantify the hydrophilicity changes of the membrane surface. Membranes surface morphology, surface and cross-sectional structures, and nanometer-particle distribution on the membrane surface were examined by atomic-force microscopy (AFM), scanning electron microscopy (SEM), and confocal laser-scanning microscopy (CLSM), respectively. Thermal analysis (DSC) was performed in order to investigate the interactions between membrane components. The effects of the nanometer Al2O3-particles concentration in the polymer dope on the permeation properties, membrane strength, and anti-fouling performance were examined. The experimental results indicated that Al2O3-PVDF composite membranes exhibit significant differences in surface properties and intrinsic properties due to nanometer-particles addition. (c) 2005 Elsevier B.V. All rights reserved.