The mechanical alloying is the most convenient method to produce Mg-Ni alloys. In this study, the effect of ball-to-powder weight ratios and the mechanical alloying time on amorphization of Mg50Ni50 alloy and its thermal stabilities were investigated. Mg50Ni50 alloy has been produced by using Spex 8000 D mixer/mill with different ball-to-powder weight ratios (5:1, 10:1, 20:1). Amorphization times by XRD analysis are found to be 60h for 5:1 ball-to-powder weight ratio, 10h for 10:1 ball-to-powder weight ratio and 5 h for 20:1 ball-to-powder weight ratio. The thermal stabilities of amorphous Mg50Ni50 alloys, obtained by different ball-to-powder weight ratios, have been determined and the effect of heating rates on the crystallization temperatures have also been investigated by DSC. The heating rates employed were 5, 10, 15, 20 degrees C/min. During the first crystallization reaction, the amorphous and Mg2Ni intermetallic phases occurred. DSC studies show that increase in heating rates increased the crystallization temperatures for all samples. The apparent activation energies were determined by means of the Kissinger method. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.