A series of polyaniline titanium dioxide (PANI/TiO2) nanocomposite film sensor were fabricated by an in-situ chemical oxidation polymerization of aniline at TiO2 (anatase) surface, and were evaluated the CO gas sensitivity under UV irradiation at room temperature. Although adding PANI into TiO2 seemed to weaken the photo-assisted conductivity of film sensor sample at N-2 atmosphere, it enhanced the photo-assisted gas sensitivity to CO. Based on the chemical characterization results of PANI/TiO2 by FT-IR, Raman and XPS, it is proposed that the protonated N site in PANI chains (formed by TiO2 interacting with PANI) would promote the adsorption of CO, resulting in the more electrons from CO to PANI by the typical pi-conjugated structures of benzenoid and quinonoid units and then to TiO2 by the hydrogen bonds (N center dot center dot center dot H center dot center dot center dot O) in the interface of PANI and TiO2. Moreover, the presence of H2O could enhance this photo-assisted gas sensitivity. Furthermore, the PANI/TiO2 powder sample also exhibited a higher activity of photocatalytic oxidizing CO than the pure TiO2 sample, indicating that the enhancement in the photo-assisted sensing response to CO would benefit the photocatalytic oxidation of CO over PANI/TiO2. This study not only provides a possible approach to develop a photo-assisted gas-sensitive material by introducing the structure of organic-inorganic hybrided nanocomposite, but also provides a possible method to estimate the photocatalytic activity of a semiconductor material by testing its photo-assisted sensitivity to the reactant gas. (C) 2017 Elsevier B.V. All rights reserved.