To improve the electrochemical cycle stability of MgNi alloy, a series of MgNi-CoSi composites were synthesized by mechanical alloying (MA). The influence of CoSi on the electrochemical properties of the MgNi alloy was investigated systematically. Electrochemical studies showed that the maximum discharge capacity of MgNi-CoSi decreased but the cycle stability improved remarkably. When the MA time was 10 h, the composite exhibited the best performance. Electrochemical impedance spectroscopy (EIS) and linear polarization results showed that the charge-transfer resistance decreased and the exchange current density increased, indicating that the electrochemical kinetics of MgNi was improved by CoSi. Moreover, according to potentiodynamic polarization, the anticorrosion behavior of MgNi was also improved. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.