Recent studies of rare-earth/magnesium/nickel alloys showed that REMgNi4-based alloys, RE(2-x)MgxNi4 (RE: rare-earth metals; 0 < x < 2), with a AuBe5-type crystal structure, exhibit reversible hydrogen absorption and desorption reactions, which are known as hydrogen storage. Hydrogen storage alloys are designed to absorb and release hydrogen without compromising their own structure. Hydrogen storage alloys represent an excellent solution for fuel cell storage.