The structure and effects of mechanical ball-milling on hydriding behavior of LaMg11Ni were studied. Structures of the alloys and the hydrides were determined by X-ray diffraction (XRD). By measuring hydrogen-storage capacity and hydrogen absorption kinetics of the material, hydriding behaviors of LaMg11Ni prepared by different mechanical ball-milling time were compared. In this work, there is a 20% increase of hydrogen absorption capacity after 20 h milling, and the kinetics of hydrogen absorption was markedly improved. Nevertheless, further milling does not make good. When the milling time is too long, the situation will be deteriorated. For example, after 120 h milling, the material has very poor hydrogen-storage capacity and is difficult to activate. Explanation of the phenomenon is proposed on the basis of microstructure analysis. (C) 2003 Published by Elsevier B.V.