A modified TiO2 was prepared by short-time annealing in low concentration of hydrogen gas at low temperature and ordinary pressure. As a result, the hydrogenated TiO2 (H-TiO2) and hydrogenated carbon-doped TiO2 (H-C-TiO2) could decompose gaseous formaldehyde without light irradiation at room temperature. Compared with pure TiO2, the H-TiO2 and H-C-TiO2 were allowed to introduce more oxygen vacancies and surface hydroxyl groups, which had crucial contribution to catalytic oxidation of gaseous formaldehyde in the dark. Moreover, the existence of oxygen vacancies and surface hydroxyl groups were confirmed by XPS and EPR. Oxygen vacancies could efficiently govern O-2 adsorption by trapping O-2 molecules on defect sites and producing active oxygen species. The surface hydroxyl groups could facilitate the adsorption of O-2 molecules and remove carbonate species which could block the catalytic active sites. Based on these results, a novel mechanism of gaseous formaldehyde decomposed by hydrogenated TiO2 in the dark was proposed. (C) 2013 Elsevier B.V. All rights reserved.