The hydrogen sorption performance of Mg is constrained by the difficulties of hydrogen dissociation on particle surface and mass transfer in particle bulk. This work focuses on oxygen vacancy and its effect on the performance of Mg-xCeO(2) (x = 0.7, 1.5, 3, and 6 mol.%) from ball milling for hydrogen storage. The HRTEM observation shows that the crystal domains of Mg from ball milling are reduced to nanoscale by the addition of hard CeO2 nano-particles. The XRD and XPS characterization shows that during heating for hydrogenation, some O atoms in CeO2 transfer to Mg and form MgO, and CeO2 converts to Ce6O11 with oxygen vacancies. The isothermal absorption (p-c-T) analysis shows that the hydrogen capacity of the materials increases with the increase of CeO2 additive, and the optimum addition is 3.0 mol.%. The DSC analysis shows that with the addition of 3.0 mol.% of CeO2, the hydrogen desorption peak temperature is 35 degrees C lower than that of pure MgH2, and the calculated activation energy deceases by 31.3 kJ/mol. The improvement of hydrogen sorption performance is mainly attributed to the formation of oxygen vacancies. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.