95%(gravity cast Mg–23.5Ni)–-5%Nb 2 O 5 alloy was prepared by horizontal ball milling in n-hexane of gravity cast Mg–23.5wt%Ni with Spex milled Nb 2 O 5 . Melt spun Mg–23.5wt%Ni after heat treatment at 523K for 1h was also ground by planetary ball milling with finer Nb 2 O 5 prepared by milling with NaCl. The activated 90%(melt spun Mg–23.5Ni)–10%Nb 2 O 5 alloy shows higher hydriding and dehydriding rates than the activated 95%(gravity cast Mg–23.5Ni)–5%Nb 2 O 5 alloy, thanks to the homogeneous distribution of fine Mg 2 Ni phase in melt spun Mg–23.5Ni and the finer Nb 2 O 5 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%Nb 2 O 5 alloy absorbs 4.70wt%H at 573K under 12bar H 2 for 10min, and desorbs 4.75wt%H at 573K under 1.0bar H 2 for 25min.