Structural investigations showed that the crystal structure influences the hydrogen storage properties of MgH2. The crystal structure and dehydriding temperature of MgH2 activated by high energy ball milling under an argon atmosphere were studied. The X-ray diffraction characterization showed that a small amount of tetragonal alpha-MgH2 phase transforms into crystalline gamma-MgH2 of an orthorhombic structure during milling, and gamma-MgH2 peak intensity increased with increasing ball milling time within a certain limit, but disappeared early in the hydrogenation cycle at a temperature of 300 degrees C. We studied the phase structure and the stability of the MgH2 during absorption/desorption cycles as well as thermal stability in a context of sustainable use of MgH2. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.