By hydrogen plasma metal reaction method, we obtained Mg, Ni, Co, Cu and Fe nanoparticles. Mg nanoparticles show larger average particle size than Ni, Co, Cu and Fe ones. From these metal nanoparticles, Mg-based hydrogen storage alloys (Mg 2 Ni, Mg 2 Co and Mg 2 Cu) and hydrides (Mg 2 NiH 4 , Mg 2 CoH 5 and Mg 2 FeH 6 ) were prepared by solid–solid and gas–solid reactions. Powder X-ray diffraction (XRD) was used to define the structure and composition information. The preparation results in different atmosphere were compared and discussed. Hydrogen and nanostructure play important roles in the preparation of Mg-based hydrogen storage alloys/hydrides in convenient conditions from metal nanoparticles.