The correlations between the structures and gas-sensing properties of porous thin-film gas sensors made of packed hollow spheres are investigated. For this purpose, hollow polymeric spheres were used as templates. Double-shell hollow spheres were prepared by encapsulating the polymeric hollow spheres with TiO(2) shells. Solid polymeric spheres were used as templates for comparison. Porous thin-film gas sensor with interconnected three-dimensional pores was prepared by using the TiO(2) encapsulated hollow spheres. The doubleshell hollow spheres and porous titania films were characterized by XRD, BET, TEM and SEM. The gas-sensing properties of the sensors toward NO(2) depend on the type of template and the three-dimensional porous structure of the films. Using the hollow sphere template and adding precursors during the film formation procedure help to prevent the collapse of hollow sphere and form the mesopores in films after removing the template. These films show enhanced gas sensitivity when compared to TiO(2) polycrystalline films. Such improvement in sensitivity results from the porous architecture of the hollow microsphere films which not only increase the active surface area but also promotes the gas diffusion. (C) 2011 Elsevier B.V. All rights reserved.