A series of Mg-Ni or Mg-Cu alloys with Mg content comprised between 55 and 77 at% Mg was prepared by mechanical alloying with the aim of synthesizing Mg2Ni and Mg2Cu phases, respectively. Their morphology and structural properties were characterized by scanning electron microscopy (SEM) and X-ray Diffraction (XRD). High Pressure Differential Scanning Calorimetry (HP-DSC) was used to evaluate their hydrogenation properties. For the Mg-Ni series, 8 hours of milling were enough to synthesize the Mg2Ni alloy. The highest reversible hydrogen capacity (2.8 mass%) was obtained for 70 at% Mg sample without the need of any activation treatment. For Mg-Cu series, 83 mass% of Mg2Cu was obtained after 4 hours of milling. From the view point of alloying composition, Mg-rich samples show better crystallinity of Mg2Cu phase. Under hydrogen, the Mg2Cu powder mixtures decompose and form MgH2 hydride storing 1.56 mass% of hydrogen for 66 at% Mg. For the Mg-Ni series, Cu or Al elements (1 to 10 mass%) were added during milling. HP-DSC runs show that they destabilize the hydride phase due to alloying effects.