The optical and structural properties of r.f. sputtered CeO2 thin films deposited on Pyrex substrates have been studied as a function of substrate temperature during deposition. The refractive index, n, extinction coefficient, k, and bandgap of the films were calculated from reflectance, R, and transmittance, T, spectra in the wavelength range 340-900 nm. The refractive index of CeO2 films at 550 nm comprises values from about 2.25-2.4 depending on the substrate temperature during deposition. The extinction coefficient was negligible for wavelength values higher than 400 nm. The value obtained for the bandgap was 3.1 eV. The X-ray diffraction patterns showed the same (fcc) cubic structure with preferential orientation depending on substrate temperature during deposition. The scanning force microscope measurements showed that the roughness and grain size of the CeO2 films increase with increasing substrate temperature.