Polyoxometalate (POM)/TiO2 (anatase phase) supramolecule composite films are synthesized and employed for studying the effects of adsorbed gas molecules on the surface resistance of films. Here the POM is the Keggin type lacunary PW11O397- polyanion. The POM/TiO2 film's responses to noxious gases such as NH3 and NO2 are much better than those of pure TiO2 films. This is attributed to the enhanced surface adsorption of gases, but also, and more importantly, to the POM's modification of the charge transfer process between the adsorbed gas and the film. Compared with pure TiO2 film, the POM/TiO2 film shows faster response and recovery time at its optimal working temperature of 430 K for NH3 and 418 K for NO2, indicating that it has great potential for gas sensitivity at lower temperatures. (C) 2003 Elsevier B.V. All rights reserved.