Mg2Ni powder was heated up to 880°C which is higher than the melting point of Mg2Ni alloys (760°C) for 30 minutes and immediately cooled into water (14°C). And then, mechanical ball milling was conducted for 1,4,8,10,12,24 hours respectively. As milling time increased discharge capacity was increased to maximum of 700mAh/g at 12hours then decreased with increasing milling time. The best high rate dischargeability (HRD) characteristic also obtain at the 12 hours ball milling time. Therefore, the ball milling time could be shorten to 12 hours by heat treatment and rapid cooling. Praseodymium (0,0.2,0.5,0.7,1.0%Pr) was added to Mg2Ni alloys. These alloys were ground for 12 hours to investigate the improvement of cycle life. The cycle life was remarkably improved with increasing the amount of Pr. The best amount of Pr was 0.7 wt%.