Metal oxide films are important for various optical devices and especially for solar energy materials. TiO2-mixed Nb2O5 thin films have been produced by sot-gel dip-coating method. Several parameters such as heat treatment, thickness, and mixture percentages are studied for the effect of the optical, structural and electrochromic properties of the materials. Optical parameters of the films were calculated through transmission and reflection measurement by a refractive index, extinction coefficient and thickness analyzer. Structural, electrochromic and surface analyses of the films were done by X-ray diffractometer, potentiostat/galvanostat and atomic force microscope systems. (c) 2004 Elsevier B.V. All rights reserved.