On the basis of catalytic actions of transition metals and rare earth metals on Mg-based hydrogen storage alloys and aiming at alleviating the adverse influence of Mg oxidation, Mg-Ni-Ce alloys with different Ni and Ce contents were prepared by near equilibrium solidification. A new 18R-type long-period stacking ordered phase (LPSO) was formed coherently with Mg, Ni-substituted Mg12Ce and Mg2Ni in Mg-rich Mg-Ni-Ce ternary alloys. Distinct from the reported LPSO structures in other Mg-based alloys, in which the LPSO structures were fundamentally long period stacking variants of hexagonal close-packed structure of Mg, the LPSO structure found in the present work was a variant of Mg12Ce. Nanocrystalline alloys were obtained by high-energy ball milling the as-cast alloys. Nanocrystals of Mg, Mg2Ni and Mg12Ce with grain size in the range of 3-5 nm were observed in ball milled samples. The activation performance, isothermal hydrogenation behavior and anti-oxidation properties of the ball milled samples were systematically investigated and corresponding mechanisms were discussed based on detailed microstructural characteristics. CeH2.73 was formed after hydrogenation and spontaneously transformed into CeO2 during air exposure. The anti-oxidation properties of Mg-based hydrogen storage alloy were substantially improved with the addition of Ce by forming CeH2.73/CeO2 composite. (C) 2016 Elsevier B.V. All rights reserved.