Abstract The hydriding combustion synthesis (HCS) of Mg 2FeH 6 and Mg 2Ni 1− x Fe x hydrides was systematically studied by changing the value of x from 0.25 to 1.0. This study aimed at improving the Mg 2FeH 6 yield in production and examining the effect of the addition of nickel to the hydrogen storage properties of the Mg 2FeH 6 hydride. In synthesizing metallic hydrides, the raw materials in metallic powders were mechanically activated by a ball mill before the HCS treatment. As a result, the ball-milled 2Mg + Fe recorded as much as 5 mass% in hydrogen storage capacity during the HCS treatment, and the final product successfully indicated a high purity Mg 2FeH 6. Interestingly, the deformation enthalpies of the Mg 2Ni 1− x Fe x hydrides were larger by 10% or more than Mg 2NiH 4 and Mg 2FeH 6, taken individually. This was collateral evidence to prove that the HCS of Mg 2FeH 6 and Mg 2Ni 1− x Fe x hydrides with ball milling (BM) produced a new structure of the Mg–Ni–Fe–H system due to the synergy effect.