Mg-Ni-C composite hydrogen storage materials were prepared by first ball milling the powder mixtures of carbon aerogel and nano-Ni, and then mixed with magnesium powder followed by hydriding combustion synthesis (HCS). The HCS product was further treated by mechanical milling for 10 h. The effect of Ni/C ratio on the structures and hydrogen absorption/desorption properties of the materials were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and pressure composition temperature (PCT) measurements. It is found that 90Mg-6Ni-4C system shows the best hydriding/dehydriding properties, which absorbs hydrogen at a saturated capacity of 5.23 wt.% within 68 s at 373 K and desorbs 3.74 wt.% hydrogen within 1800 s at 523 K. Moreover, the dehydriding onset temperature of the system is 430 K, which is 45 K lower than that of 90Mg-10Ni system or 95 K lower than that of 90Mg-10C system. The improved hydriding/dehydriding properties are related greatly to the Ni/C ratio and the structures of the composite systems. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.