Mixed vanadium tungsten oxide thin films were grown in oxygen atmosphere using pulsed laser deposition. With the oxygen pressure fixed to an optimized value of 10 (-1) mbar, the influence of the substrate temperature and the film composition (i.e., vanadium content) on the electrochromism properties were studied. Whatever the film composition, films deposited on SnO2:F coated glass substrate were amorphous when deposited at room temperature while W-V-O (V<20%) films, deposited at 400C, exhibited X-ray characteristics similar to those of monoclinic WO3, suggesting a W1 - xVxO3-y solid solution. As a general trend, when V-based WO3 films cycle in protonic medium, both the cell capacity and the coloration efficiency decrease as the vanadium content increases. Upon very early cycling, a preferred reduction of the vanadium ions is observed with no further oxidation. Films containing a low amount of vanadium were more neutral in color than pure tungsten oxide. (C) 2001 The Electrochemical Society. All rights reserved.