Optical and electrochromic properties of sol-gel dip-coated Nb2O5 and WO3-doped Nb2O5 thin films were investigated. Niobium ethoxide, ethanol and acetic acid were used as precursors for the Nb2O5 sol. Tungsten chloride and 2-propanol were used for preparing the WO3 sol. Various percentages of WO3 were mixed with the Nb2O5 sol to obtain WO3-doped Nb2O5 thin films. Their optical, structural and electrochromic properties were investigated by spectrophotometry, XRD, SEM and cyclic voltammetry. (C) 2003 Elsevier B.V. All rights reserved.