The effect of La/Ni ratio on hydrogen storage properties of Mg(88.5)Ni(x)La(y) (x+y = 11.5, y/x = 0, 1/16, 1/4, 1/2 and 2/1) composites prepared by hydriding combustion synthesis followed by mechanical milling was investigated. It was found that Mg(88.5)Ni(x)La(y) (y/x = 1/16) composite showed the largest hydrogen absorption capacity of 4.45 wt % in 30 s at 373 K among the composites. Compared with the other composites, Mg(88.5)Ni(x)La(y) (y/x = 1/16) had the rapid dehydriding rate during heating though the initial dehydriding temperatures of all the composites were almost the same and approximately 460K. XRD analysis indicated that Mg-Ni-La composites contained Mg, MgH(2), Mg(2)NiH(0.3), Mg(2)NiH(4) and LaH(2). From the analysis of pressure-concentration isotherms, the existence of LaH(2) resulted in the increased hydrogen storage capacity in Mg(88.5)Ni(x)La(y) (y/x = 1/16) composite. It was demonstrated that the excellent hydrogen storage properties of Mg(88.5)Ni(x)La(y) (y/x = 1/16) were attributed to the effective synergetic catalysis of LaH(2) and Mg(2)Ni. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.