Hydrogenation properties of the MmNi(4.5)Al(0.5)Zr(x) (x = 0-0.2) alloys are investigated by means of P-C-isotherm measurements, X-ray diffractometry, scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). As the Zr content increases, the first hydriding reaction is completed in a shorter rime, but the plateau pressure is sloped and decreases. At a composition of x = 0.05, a maximum hydrogen storage capacity is obtained with a enhanced activation property. Upon pressure cycling of the MmNi(4.5)Al(0.5)Zr(0.5) alloy, the hydrogen storage capacity is decreased by only 8% after 4300 cycles. From the X-ray diffraction, SEM and EDX tests, new second phases are observed at high Zr content above x = 0.1. The major second phase is confirmed to be the ZrNi3 phase. It is considered that the improved activation properties of the MmNi(4.5)Al(0.5)Zr(x) alloys are caused by the strong catalytic effect of ZrNi, on the dissociative chemisorption of hydrogen molecule. Among the investigated alloy systems, it is suggested that the most suitable alloy is the MmNi(4.5)Al(0.5)Zr(0.05) as a new hydrogen storage material due to its the large hydrogen storage capacity, the improved activation behavior and the strong resistance to the degradation in the subsequent cyclic operation.