To improve the hydrogen storage performance of PrMg12-type alloys, Ni was adopted to replace partially Mg in the alloys.The PrMg11 Ni+x wt.% Ni (x=100, 200) alloys were prepared via mechanical milling.The phase structures and morphology of the experimental alloys were in-vestigated by X-ray diffraction and transmission electron microscopy.The results show that increasing milling time and Ni content accelerate the formation of nanocrystalline and amor-phous structure.The gaseous hydrogen storage properties of the experimental alloys were de-termined by differential scanning calorimetry (DSC) and Sievert apparatus.In addition, in-creasing milling time makes the hydrogenation rates of the alloys augment firstly and decline subse-quently and the dehydrogenation rate always increases.The maximum capacity is 5.572 wt.% for the x=100 alloy and 5.829 wt.% for the x=200 alloy, respectively.The enthalpy change (ΔH), entropy change (ΔS) and the dehydrogenation activation energy (Edek ) markedly lower with in-creasing the milling time and the Ni content due to the generation of nanocrystalline and amorphous structure.