CeO2-SiO2 composite thin films were prepared by e-beam evaporation and ion beam assisted deposition using an End-Hall ion source. The refractive index of composite thin films exhibited a maximum value at 20%-35% SiO2 fraction, indicating the high packing density. Optical analysis revealed that the transmittance and reflectance spectra of composite films were consistent with the results of the refractive index. The results from x-ray diffractometry, atomic force microscopy and scanning electron microscopy measurements showed that composite thin films containing 20%-35% SiO2 concentration had a dense and smooth amorphous surface, compared to the roughened granular structure of the pure SiO2 and CeO2 thin films. The composite thin films with 20%-35% SiO2 concentration exhibited a higher resistance to water absorption than the CeO2 thin films in spite of the highest refractive index. (C) 2004 American Institute of Physics.