The amorphous Mg-Al-Ni composites were prepared by mechanical ball-milling of Mg17Al12 with x wt.%Ni (x=0, 50, 100, 150, 200). The effects of Ni addition and ball-milling parameters on the electrochemicalhydrogen storage properties and microstructures of the prepared composites have been investigated systematically.For the Mg17Al12 ball-milled without Ni powder, its particle size decreases but the crystalstructure does not change even the ball-milling time extending to 120 h, and its discharge capacity is lessthan 15 mAh g_1. The Ni addition is advantageous for the formation of Mg-Al-Ni amorphous structureand for the improvement of the electrochemical characteristics of the composites. With the Ni contentx increasing, the composites exhibit higher degree of amorphorization. Moreover, the discharge capacityof the composite increases from 41.3mAh g_1 (x=50) to 658.2 mAh g_1 (x=200) gradually, and theexchange current density 10 increases from 67.1mA g_1 (x=50) to 263.8mA g_1 (x=200), which is consistentwith the variation of high-rate dischargeability (HRD). The ball-milled Mg17Al12+200 wt.% Nicomposite has the highest cycling discharge capacity in the first 50 cycles.