MgH2 nanocomposites with ZrCrNi alloy obtained by high energy ball-milling were studied as-milled and after several hydriding-deydriding cycles. The microstructure and morphology of the samples was characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns show that no phase formation between MgH2 and elements of the alloys takes place during milling and after cycling. Different morphology of the powders as-milled and after cycling was observed by SEM. Pressure-composition isotherms of these composites were obtained in the pressure and temperature range of 0.1-15 bar and 200-300 degrees C respectively. The maximum reversible storage capacity was found to be 6.2 wt% at 300 degrees C. Absorption/desorption kinetics data at pressures of 0.1-5.0 bar and temperatures of 275 degrees C and 300 degrees C show that an activation process of about 20 cycles at 300 degrees C is necessary for stabilization of the kinetics and for achievement of the full hydrogen capacity. The thermodynamic parameters, i.e. enthalpy of formation and dissociation calculated using Van't Hoff plots, were found to be 73.53 kJ mol(-1) and 87.63 kJ mol(-1) respectively, in agreement with MgH2 data reported in literature. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.