An MgH2 + 1 mol% Nb2O5 system was modified by heptane and acetone through a high-energy ball milling process, and their rehydrogenation performances were investigated. XRD results indicated that except MgH2 and Nb2O5 phases Mg and MgO phases existed after ball milling. The rehydrogenation results showed that after modification by heptane the capacity increased from 3.0 wt% and 4.2 wt% to 5.0 wt% and 5.5 wt% within 110 s at 523 K and 573 K, respectively. The hydriding rate increased from 0.08 wt%/s after 20 s to 0.22 wt%/s after 10 s at 523 K. However, after modification by acetone it only absorbed 1.8 wt% and 2.0 wt% of hydrogen even within 8000 s at 523 K and 573 K, respectively. Rietveld refinement results indicated that after modification by the heptane the content of MgO was reduced from 6.8 wt% to 4.2 wt%, while after the modification by the acetone the content of MgO was significantly increased from 6.8 wt% to 23.8 wt%. The difference in the rehydrogenation performance was believed to be attributed to the different contents of the MgO phase, which led to the difference in the contents of the MgH2 phase. It implied that the heptane acted as a solvent without oxygen element in it to prevent the MgH2 + Nb2O5 system from aggregation, crystallization and oxidation. It suggested heptane was suitable for the improvement of the rehydrogenation performance of MgH2 system. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.