95%(gravity cast Mg-23.5Ni)-5%Nb2O5 alloy was prepared by horizontal ball milling in n-hexane of gravity cast Mg-23.5wt%Ni with Spex milled Nb2O5. Melt spun Mg-23.5wt%Ni after heat treatment at 523 K for 1 h was also ground by planetary ball milling with finer Nb2O5 prepared by milling with NaCl. The activated 90%(melt spun Mg-23.5Ni)-10%Nb2O5 alloy shows higher hydriding and dehydriding rates than the activated 95%(gravity cast Mg-23.5Ni)-5%Nb2O5 alloy, thanks to the homogeneous distribution of fine Mg2Ni phase in melt spun Mg-23.5Ni and the finer Nb2O5 addition to melt spun Mg-23.5Ni, which leads to the effective diminution of the Mg particle size. The activated 90%(ms Mg-23.5Ni)10%Nb2O5 alloy absorbs 4.70 wt%H at 573 K under 12 bar H-2 for 10 min, and desorbs 4.75 wt%H at 573 K under 1.0 bar H-2 for 25 min. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.