We performed density functional theory (DFT) based calculations to investigate the effects of O-vacancies on the adsorption of O2 on anatase TiO2(001). Our calculation results show that we can promote O2 adsorption on an initially inert stoichiometric TiO2(001) by introducing O-vacancy. The resulting excess electrons from the introduction of the O-vacancy redistribute around the neighboring Ti ions. An incoming O2 can then adsorb at the O-vacancy site, either in the superoxide state (O2-) or the peroxide state (O22 -). In the O2- state, the OO bond is oriented parallel to the surface, along [010]. In the O22 - state, the OO bond is oriented perpendicular to the surface, along [001]. Healing of the surface occurs when one of the O atoms of the perpendicularly adsorbed O2 fills the vacant site and the other atom diffuses, recovering the stoichiometric surface.