Compositional dependences of the optical properties of sol-gel derived ZrO2-TiO2 composite films (with molar ratio of Ti:Zr ranging from 0:10 to 10:0) have been studied. The refractive index, absorption coefficient, and optical band gap were determined from the corresponding transmission spectra based on Swanepoel's method. It was found that the optical properties of the composite films could be easily tailored in a wide range by a simple control on the system composition. As the molar ratio of Ti:Zr increased from 0:10 to 10:01 a clear increase of the refractive index from 1.912 to 2.263 (at 633 nm) was observed. Simultaneously, the optical band gap decreased monotonically from 5.26 to 3.25 eV Combined with the X-ray diffraction analysis, the observed variations in both the refractive index and optical band gap have been directly correlated with the structural evolution of the composite films. (C) 2007 Elsevier B.V. All rights reserved.