This work describes the use of template synthesis to produce materials with optimized properties to be used in electrochromic devices. A composite prepared by the inclusion of polyaniline within the pores of a cellulose acetate was used as primary electrochromic layer and a porous V2O5 phase was used as an auxiliary electrode to counter balance the charge in the entire device. The device closed with a gel polymer electrolyte exhibited a very high optical contrast (light yellow to dark blue) with DeltaT(750) (nm) = 78%. However, the optical response time indicates a slow ion exchange during electrochromic cycles. By comparing the voltammogram and the curve obtained by differentiation of the absorbance variation with time, it was possible to identify the contribution of each redox couple to the total color change. (C) 2004 Elsevier B.V. All rights reserved.