This paper is concerned with the functions of crystallitic carbon, prepared from anthracite coal by demineralization and carbonization, for making Mg-based nanocomposites for hydrogen storage by reactive milling under hydrogen atmosphere. The TEM and XRD analysis show that in the presence of 30 wt.% of crystallitic carbon, the Mg easily hydrided into beta-MgH2 of particle size 20-60 nm and crystal grain size 29.7 nm and a small amount of gamma-MgH2 after 3 h of milling under 1 MPa H-2. The hydrogen content of the composites is up to 5.81 wt.% determined by water displacement method, and its dehydrogenation peak temperature is 344.2 degrees C by DSC analysis. The enthalpy and entropy changes of the hydrogen desorption reaction are 42.7 kJ/mol and 80.7 J/mol K, respectively, calculated by the van't Hoff equation from the p-C-T data in 300-380 degrees C. With the extension of milling time, more gamma-MgH2 yielded, and the endothermic peak of gamma-MgH2 separated from that of beta-MgH2. The C-H dangling bonds in the hydrogenated carbon were determined by FT-IR analysis. The dehydrogenation temperature of the materials decreased with the addition of Co, Ni, Fe and Al. (C) 2012 Elsevier Ltd. All rights reserved.