The hydrogen sorption behavior of the MgFeH- MgH hydride system is investigated via in-situ synchrotron and laboratory powder X-ray diffraction (SR-PXD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), particle size distribution (PSD) and volumetric techniques. The MgFeH-MgH hydride system is obtained by mechanical milling in argon atmosphere followed by sintering at high temperature and hydrogen pressure. In-situ SR-PXD results show that upon hydriding MgH is a precursor for MgFeH formation and remained as hydrided phase in the obtained material. Diffusion constraints preclude the further formation of MgFeH . Upon dehydriding, our results suggest that MgH and MgFeH decompose independently in a narrow temperature range between 275 and 300 C. Moreover, the decomposition behavior of both hydrides in the MgFeH-MgH hydride mixture is influenced by each other via dual synergetic-destabilizing effects. The final hydriding/dehydriding products and therefore the kinetic behavior of the Mg FeH-MgH hydride system exhibits a strong dependence on the temperature and pressure conditions.