In this paper, the hydrolysis properties for hydrogen generation by Mg-metal chlorides composites in pure water are investigated. The composites were prepared by high energy ball milling. It is found that the Mg-metal chlorides composites are very promising for hydrogen generation by hydrolysis reaction. The micro-galvanic cell formed by Mg and the other metal which produced by replacement reaction occurred during the ball-milling process is very effective for improving the hydrolysis reactivity. Based on the investigations of different kinds of chlorides additives, it is found that the Mg-10 wt% FeCl3 composite ball-milled for 30 min has the best hydrolysis properties with an initial hydrogen generation rate of 1479.1 ml*g(-1) min(-1) and a theoretical hydrogen production yield of 98% in 2 min. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.