Standard and mesoporous sol-gel tungsten oxide thin films were prepared by a spin-coating technique from an ethanolic solution of tungsten hexachloride. A block copolymer (BASF(TM) Pluronic P-123) was employed as a template to generate the mesoporous structure. An ultraviolet (UV) illumination method was employed to remove the polymer templates at room temperature. The electrochromic and optical properties of the mesoporous films are described and compared to standard sol-gel tungsten oxide films. Results are also presented on the samples prepared by thermal treatment. We demonstrate that the LN illumination/ozone treatment is a superior method to remove templates which enables us to more effectively investigate the effect of mesoporosity on the electrokinetics of ion insertion into tungsten oxide films. (C) 2002 Elsevier Science B.V. All rights reserved.