In order to improve the hydrogen storage capacity and the activation properties of the hydrogen storage alloys, the rare-earth metal alloy series, MmN i 4.5 M n 0.5 Z r x (x=0, 0.025, 0.05, 0.1), are prepared by adding excess Zr in MmN i 4.5 M n 0.5 alloy. The various parts in hydrogen storage vessel consisted of copper pipes reached the setting temperature within 4~5 minutes after heat addition, which indicated that storage vessel had a good heat conductivity required in application. The performance test on storage vessel filled with rare-earth metal alloys of 1000 gr was also conducted after hydrogen charging for 10 min at 18 ? C under 10 atm. It showed that the average capacity of discharged hydrogen volume was found to be for MmNi 4.5 Mn 0.5 and MmNi 4.5 Mn x 0.5/ Zr samples indicated that the released amount of hydrogen for this AB 5 type alloys was more than 92 % of theoretic value, and also it was found that the optimum discharging temperature for obtaining an appropriate pressure of 3 atm was determined to be V ? C for MmNi 4.5 Mn 0.5 Zr x (x=0, 0.025, 0.05, 0.1) hydrogen storage alloys. The released amount of these hydrogen storage samples was 125 ℓ , 122.4 ℓ and 108.15 ℓ /kg for MmNi 4.5 Mn 0.5 Zr 0.025 MmNi 4.5 M n 0.5 Z r 0.05 , and MmN i 4.5 Mn_0.5 Zr 0 , at 70 ? C respectively. Amount of the 2nd phases increase with increase on Zr contents in MmNi 4.5 Mn 0.5 Zr 0.1 / alloy. This phenomenon indicates that ZrNi 3 in MmNi 4.5 Mn 0.5 Zr x / phase, which shows the maximum storage capacity and the strong resistance to intrinsic degradation, is considered as a proper alloy for hydrogen storage. As the Zr contents increase, the activation time and the plateau pressure decreases and sloping of the plateau pressure increases.