Abstract: Hydrogen activation plays a pivotal role in hydrogenation reactions over transition metal oxide catalysts. Clarifying hydrogen activation over ceria oxide (CeO₂) is an important issue in the acetylene hydrogenation reaction. Employing density functional theory (DFT) calculations, we studied hydrogen activation over stoichiometric and defective CeO₂(111), (110), and (100) surfaces. Hydrogen dissociates on the stoichiometric CeO₂ surfaces only forming hydroxyl groups. The presence of oxygen vacancies can promote the H₂ activation over the defective CeO₂ surfaces. Both H⁺ and H^- species can be found on the defective CeO₂(111) and (100) surfaces, whereas only H⁺ species can be observed on the defective CeO₂(110) surface. The structure sensitivity of the H₂ activation over the stoichiometric and defective CeO₂ surfaces is correlated with H⁺ and H^- adsorption energies determined by the ability of the surface oxygen vacancy formation and charge distributions of Ce and O ions. Our work provides more insight into H₂ activation on CeO₂-based catalysts which will guide better catalyst design for hydrogenation reactions.