In order to improve the hydrogen storage capacity and the activation properties of the hydrogen storage alloys, the rare-earth metal alloy series, MmNi 4.5 Mn 0.5 Zr x (x=0, 0.025, 0.05, 0.1), are prepared by adding the excess Zr in MmNi 4.5 Mn 0.5 / alloy for the strong resistance to intrinsic degradation. The hydrogen storage alloys of rare-earth metal such as LaNi 5 , and MmNi 5 X and MmNi 4.5 / M n0.5 alloys which substituted La by misch metal properties were characterized as well. The hydrogen storage alloys were produced by melting each metal mixture in arc melting furnace, and the as-cast alloys were heat-treated at 1100 ? C for 10 hr. The major elements of misch metal(Mm) were La, Ce, Pr and Nd with some impurities less than 1wt.% determined by ICP-AES. X-ray diffraction indicated that the structure for these samples was a single phase of hexagonal with CaCu 5 type. As the Zr contents increases, the activation time and the plateau pressure decrease and sloping of the plateau pressure increase. Amount of the 2nd phases increases with increase in Zr contents in MmNi 4.5 Mn 0.5 Zr 0.1 alloy, This phenomenon indicated that ZrNi 3 in this phase, which shows the maximum storage capacity and the strong resistance to intrinsic degradation, is considered as a proper alloy for hydrogen storage.