Two different procedures to stabilize the precursor NbCl5 have been applied to obtain Nb2O5 thin films by spray pyrolysis. Depending on the procedure used, determined by the way in which the precursor solution was injected into the air stream of the spray nozzle, niobium oxide thin films with different surface morphologies can be obtained. The structural properties of the Nb2O5 thin films depend on the post-annealing temperature because as-deposited films are amorphous, independently of the synthesis procedure used. The electrochromic behaviour has been estimated for all films, where monochromatic colouration efficiency (at 660 nm) of 25.5 cm(2)/C and a cathodic charge density close to 24 mC/cm(2) were found to give the best results to date for niobium oxide thin films obtained by spray pyrolysis. (C) 2008 Elsevier B.V. All rights reserved.