Mg85-Nix/MWNTs15-x (x=3, 6, 9, 12, mass fraction) alloys were prepared from Mg and multi-wall carbon nanotubes supported nickel (Ni/MWNTs) by the combined methods of hydriding combustion synthesis (HCS) and mechanical milling (MM). The crystal structures, surface morphologies and hydriding/dehydriding properties of the products were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and gas reaction controller (GRC), respectively. The results show that the Mg85-Ni9/MWNTs6 alloy possesses the best hydriding/dehydriding properties, which absorbs nearly the saturated hydrogen capacity of 5.68 wt% within 100 s at 373 K, and desorbs 4.31 wt% hydrogen within 1800 s at 523 K. The addition of Ni/MWNTs plays a catalytic role, and it takes the effect on nano-confinement of the Mg2NiH4 particles in the product. There is synergic catalysis between Ni and MWNTs, and when the mass ratio of Ni/MWNTs = 3/2, the hydriding/dehydriding properties of the Mg-Ni/MWNTs system reach the best