Greatly stable thermodynamics and sluggish kinetics impede the practical application of Mg-based hydrogen storage alloys. The modifications of composition and structure are important strategies in ting these hydrogen storage properties. In this study, Mg-based Mg90Ce5Sm5 tary alloy fabricated by vacuum induction melting was investigated to explore the performance and the reaction mechanism as hydrogen storage material by X-ray diffraction (XRD), scanning electron microscope (SEM), trans-mission electron microscopy (TEM) and pressure-composition isotherms (PCI) measurements. The re-sults indicate that the Mg-based Mg90Ce5Sm5 tary alloy consists of two solid solution phases, including the major phases (Ce, Sm)5Mg41 and the minor phases (Ce, Sm)Mg12. After hydrogen ab-sorption, these phases transform into the MgH2 and (Ce, Sm)H2.73 phase, while after hydrogen desorp-tion, the MgH2 transforms into the Mg phase, but the (Ce, Sm)H2.73 phases are not changed. The alloy has a reversible hydrogen capacity of about 5.5 wt％ H2 and exhibits well isothermal hydrogen absorption kinetics. Activation energy of 106 kJ/mol was obtained from the hydrogen desorption data between 573 and 633 K, which also exhibits the enhanced kinetics compared with the pure MgH2 sample, as a result of bimetallic synergy catalysis function of (Ce, Sm)H2.73 phases. The rate of hydrogen desorption is controlled by the release and recombination of H2 from the Mg surface. Furthermore, the changes of enthalpy and entropy of hydrogen absorption/desorption were calculated to be -80.0 kJ/mol H2,-137.5 J/K/mol H2 and 81.2 kJ/mol H2, 139.2 J/K/mol H2, respectively.