Hydro-reactive Mg-Al mechanical alloy materials are prepared by high-energy milling. Scanning electron microscopy (SEM), thermogravimetric (TG) and powder X-ray diffraction (XRD) techniques are used to characterize the materials. Their hydrolysis properties are studied in seawater by measuring the hydrogen volume produced and by calculating the rate of hydrogen evolution. The collected reaction products are analyzed after hydrolysis. The experimental results show that there are the squashed. overlapped and fined steps for metal powder in the milling progress. As the milling time increases from 0 to 4 h, the initial oxidization temperature of Mg-Al mechanical alloy materials first increases, and then decreases. An increase in milling time is found to improve the hydrogen generation rate and the hydrogen yield during hydrolysis. When the milling time reaches 4 h, the hydrolysis reaction is immediately noticeable, generating 397 mL(min g)(-1) of hydrogen within the first second minutes, and the total hydrogen evolution is 950 mL of hydrogen, or 97.1% of the theoretical yield. (C) 2012 Elsevier B.V. All rights reserved.