Ternary eutectic Mg76.87Ni12.78Y10.35 (at. %) ribbons with mixed amorphous and nanocrystalline phases were prepared by melt spinning. The microstructures of the melt-spun, hydrogenated and dehydrogenated samples were examined and compared by X-ray diffraction and transmission electron microscopy. The amorphous structure transforms into a thermally stable nanocrystalline structure with a grain size of about 5 nm during hydrogen ab/desorption cycles. The Mg, Mg2Ni and phases with Y in the melt-spun state transform into MgH2, Mg2NiH4, Mg2NiH0.3, YH2 and YH3 after hydrogenation, and transform back to Mg, Mg2Ni and YH2 upon subsequent dehydrogenation. The reaction enthalpy ((sic)H) and entropy ((sic)S) of the higher plateau pressure corresponding to Mg2Ni hydride formation are -53.25 kJ mol(-1) and -107.74 J K-1 mol(-1), respectively. The amorphous/nanocrystalline structure effectively reduces the enthalpy and entropy of Mg2Ni hydride formation, but has little effect on Mg. The activation energy for dehydrogenation of the hydrogenated ribbons is 69 kJ mol(-1). This suggests that Mg-Ni-Y with ternary eutectic composition can form an amorphous/nanocrystalline structure by melt spinning, and this nanostructure efficiently improves the thermodynamics and kinetics for hydrogen storage. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.