In this paper, ZnO nanoparticles were prepared by a sot-gel method and sensitized by azo pigment (4,4'-2-{N-[beta-hydroxyl-gamma-(rho-nitroanilino)naphthyl]}azodiphenyl) . Measurements of surface photocurrent by comb-like electrode and He-Ne laser and gas adsorption were performed on the ZnO/azo system. The process of photoinduced charge transport from excited dyes to nanocyrstalline ZnO was studied by surface photocurrent response (SPR). We have also discussed different effects of water and oxygen as gas adsorbates on SPR. Such a research should be valuable for the practical application of ZnO nanoparticles to semiconductor gas sensors. (C) 2004 Elsevier B.V. All rights reserved.