Polysulfone (PSF) is a kind of membrane material with better performance and broadly applied in water purification, biochemistry separation, Chinese traditional herb drugs extraction and concentration, etc. But PSF membrane has a tendency to be contaminated for its hydrophobicity, which can result in declining of flux and life of the membrane. To enhance the capability of PSF membrane, such as tensile strength, hydrophilic property, anti-fouling ability, novel organic-inorganic composite membranes were prepared by a process of adding modified nanosilica with higher activity and hydrophilic property to the porous matrix of PSF. Ce-doped nonstoichiometric nanosilica (modified nanosilica) was synthesized by doping the rare earth Ce element. Composite membranes were prepared by sol-gel process and characterized by test of tensile strength, contact angel, porosity, infrared spectroscope (IR), environment scanning electron microscope (ESEM) and performance for oil-water separation. The results show that tensile strength is improved to a large extent and contact angel reduces from 78.6 degrees to 41.7 degrees; porosity reaches 75%. IR spectrum of the composite membrane indicates that the cerium element has entered into the framework of nanosilica. ESEM micrographs indicate that the composite membrane owning the asymmetry structure has two layers of compact layer and porous layer and that modified nanosilica is uniformly dispersed in PSF. The flux in treatment of wastewater containing oil is greatly increased, so it indicates that the antifouling ability is significantly enhanced and treatment of wastewater containing oil using the composite membrane developed is feasible and desirable. (C) 2008 Elsevier B.V. All rights reserved.