We report on the quantum chemical study of magnesium(Mg)/magnesium–hydrogen(Mg–H) nanowires with the diameter of ∼1nm. The Mg–H nanowire, which is formed by loading H atoms on the surface of Mg nanowire, exhibits the same hydrogen-storage capacity as that of bulk stoichiometric MgH 2 (7.6wt%) but a significant low desorption enthalpy of 37.55kJ/mol H 2 , which corresponds to an ambient-close desorption temperature of 287K. The subsequent investigations of electronic structure and stability of the Mg–H nanowires reveal that the strength of Mg–H interaction can be further adjusted by considering the H-content and size effects. These results show that the Mg/Mg–H nanowires with the diameter of ∼1nm are promising for hydrogen storage due to the proper hydride thermodynamics.