Abstract: MgH₂ with a large hydrogen capacity is regarded as a promising hydrogen storage material. However, it still suffers from high thermal stability and sluggish kinetics. In this paper, highly dispersed nano-Ni has been successfully prepared by using the polyol reduction method with an average size of 2.14 nm, which significantly improves the de/rehydrogenation properties of MgH₂. The MgH₂–10wt% nano-Ni sample starts releasing H₂ at 497 K, and roughly 6.2wt% H₂ has been liberated at 583 K. The rehydrogenation kinetics of the sample are also greatly improved, and the adsorption capacity reaches 5.3wt% H₂ in 1000 s at 482 K and under 3 MPa hydrogen pressure. Moreover, the activation energies of de/rehydrogenation of the MgH₂–10wt% nano-Ni sample are reduced to (88 ± 2) and (87 ± 1) kJ·mol⁻¹, respectively. In addition, the thermal stability of the MgH₂–10wt% nano-Ni system is reduced by 5.5 kJ per mol H₂ from that of pristine MgH₂. This finding indicates that nano-Ni significantly improves both the thermodynamic and kinetic performances of the de/rehydrogenation of MgH₂, serving as a bi-functional additive of both reagent and catalyst.