Nanometer Ce3+-doped SiO2 was prepared by sol-gel method, and it is photoluminescent property was studied. The structure of samples was found to be amorphous with powder size between 20 and 30 nm determined by X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques. The photoluminescence spectrum of the Ce3+-doped SiO2 annealed at 450 ℃ shows a very strong UV luminescence band at 346 nm under 230 nm excitation. A wide band with multipeaks was also observed under the excitation of 380 nm. Compared with the Cu2+-doped and undoped silica a conclusion can be drawn that the UV luminescence band at 346 nm is originated from the natural defect of silica but not the characteristic luminescence of d-f transition of Ce3+. Based on the relationship of 346 nm band emission intensity with the heat treatment temperature and the concentration of Ce3+ ions in SiO2, the structure model of the 346 nm band was discussed.