The electrochemical characteristics of the ball-milled NdMg12 alloys with Ni powders were investigated. The first discharge capacity of the ball-milled sample was improved from 770 to 1200mAh/g when the Ni content in the alloy was increased from 150 to 200wt%. Furthermore, the first discharge capacity of the ball-milled NdMg12 + 200 wt% Ni composite was very close to that of the ball-milled PrMg12 + 200 wt% Ni composite. However, the high rate dischargeability of the former was not as good as that of the latter. Further analysis by electrochemical impedance spectroscopy (EIS) technique reveals a larger reaction resistance in the ball-milled NdMg12+200wt% Ni composite, probably due to the formation of Nd oxide or Nd(OH)3 film on the surface of alloy. Larger reaction resistance resulted in the lower high rate dischargeability of this sample. In addition, the ball-milled NdMg12 + 200 wt% Ni composite exhibited better cycle performance due to the existence of the corrosion resistant Nd oxide or Nd(OH)(3) film. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.