A comparative study based on MgH2 ball-milled with altered Ni particle sizes under different conditions was conducted to reveal the effect of close contact between hydrides and metal catalysts on their hydrogen sorption properties.It is found that the Mg + nano-Ni (5 at％) composites not only exhibit a substantial decreased onset desorption temperature by approximately 180 ℃ but also dramatically enhance the absorption kinetics by sixteen times in comparison with those of pure MgH2.This remarkable kinetics enhancement can be explained by the superior catalytic effect of Ni present in composites that highly depends on its particle size and its close contact with MgH2.