In order to improve the hydrogen-storage properties of magnesium, oxides, metallic element(s) and a hydride-forming element were added to Mg by grinding under a hydrogen atmosphere (reactive mechanical grinding). As the oxides, Fe 2 O 3 purchased, Fe 2 O 3 prepared by spray conversion, MnO purchased, SiO 2 prepared by spray conversion, and Cr 2 O 3 prepared by spray conversion were chosen. As the metallic elements, Ni, Fe, and Mo were selected. In addition, as the hydride-forming element, Ti was selected. Samples with the compositions of Mg–10wt%oxide, 76.5wt%Mg–23.5wt%Ni, 71.5wt%Mg–23.5wt%Ni–5wt% Fe 2 O 3 , 71.5wt%Mg–23.5wt%Ni–5wt%Fe, and Mg–14wt%Ni–2wt%Fe–2wt%Ti–2wt%Mo were prepared. The hydrogen-storage properties and changes in phase and microstructure after the hydriding–dehydriding cycling of the prepared samples were then investigated.