A study is carried out on the role of additives for structural refinement of magnesium powders in mechanical milling. Additives, namely Al2O3, SiC, V and graphite are chosen so as to cover a wide hardness range. Structural refinement after milling is studied both metallographically and in terms of X-ray line broadening. It is found that for efficient structural refinement, the additives should be chosen not on the basis of their hardness but rather whether or not they are preserved with an acceptable size during milling. Thus, of the additives, it is found that graphite and Al2O3 are most effective. The milled structures are modified upon exposure to hydrogenation temperature, leading to similar structural sizes. In terms of hydrogenation, graphite appears to be the most effective additive. A storage capacity of 6.0 wt% is reached with a quite fast sorbing rate. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.