Single-walled carbon nanotubes (SWNTs) were mechanically milled with LiBH4/MgH2 mixture, and examined with respect to its effect on the reversible dehydrogenation properties of the Li-Mg-B-H system. Experimental results show that the addition of SWNTs results in an enhanced dehydriding rate and improved cyclic stability of the LiBH4/MgH2 composite. For example, the LiBH4/MgH2 composite with 10 wt% purified SWNTs additive can release nearly 10 wt% hydrogen within 20 min at 450 degrees C, with an average dehydriding rate over 2 times faster than that of the neat LiBH4/MgH2 sample. Based on the results of phase analysis and a series of designed experiments, the mechanism underlying the observed property improvement was discussed. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.