Hydrogen sorption by magnesium-carbon composites during reactive high-energy ball milling under hydrogen was investigated. Mg-based composites absorb up to 5 wt.% of hydrogen during milling. It was found that reactive ball milling of magnesium with the different carbon allotropes (graphite, ultrafine diamonds, carbon nanotubes and amorphous carbon powder produced by electric breakdown of organic liquids) leads to a significant increase of hydrogen sorption rate. Morphology and phase composition of the synthesized Mg-C composites have been studied by TEM and XRD. Special attention was focused on the study of structural changes in the carbon additives. The hydrogenation rate of magnesium-carbon composites during reactive ball milling is strongly affected by the nature of carbon additives and their dispersion in an initial state. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.