Optical properties of zirconium oxide films on glass substrates deposited by thermal oxidation method have been studied at different temperatures. Optical characteristics of films such as refractive index, extinction coefficient, average thickness and optical dielectric constants were calculated using Swanepoel's method. X-ray diffraction analysis (XRD) and atomic force microscopy were performed to investigate the film structure and morphology. It was found out that the optical properties of zirconium oxide films are affected by oxidation temperature which are due to changes of film microstructure and surface roughness. (C) 2013 Elsevier B.V. All rights reserved.