Using the sot-gel method a series of nonstoichiometric nanosilica doped with the rare earth element Ce (CexSi1-xO2-delta, x=0.0-0.14) were prepared in order to modify the physicochemical properties of the nanosilica surface and to enhance the strength of the Ce-nanosilica/polysulfone composite membranes. The Cex-Si1-xO2-delta samples were characterized by Fourier transform infrared spectra, X-ray diffraction and X-ray photoelectron spectra. The observations from these characterizations suggest that most Ce atoms enter the silica framework to form a Ce-O-Si solid solution while the cubic CeO2 phase is segregated when x>0.08. Transmission electron microscopy images show that CexSi1-xO2-delta particles are spherical with a uniform size distribution in the range of 30-50 nm and contain some inner pores with sizes up to a few nanometers. Specifically, Ce0.08Si0.92O2-delta- 700 calcined at 700 degrees C shows the biggest surface area, the smallest pore size and the highest hydrophilicity, which makes the Ce0.08Si0.92O2-delta/polysulfone composite membranes (8.0 wt%) exhibit the strongest mechanical strength (3.223 MPa), which is enhanced by more than 100% in comparison with the pure polymer membrane.