Amorphous CoB was prepared by chemical reduction method. The influence of CoB on the electrochemical properties of MgNi alloy was investigated. MgNi-CoB composite was prepared by mechanical alloying MA, The cycle life of the electrodes was improved by CoB, The ( morphology of the material was modified by CoB. The MgNi-CoB (weight ratio 100: 15) composite which was MA 15 h exhibited the best electrochemical performance. The hydrogen diffusion coefficient in MgNi was increased by CoB (D-H = 1. 195 x 10(-10) cm(3) g(-1)). The exchange current density I-0 increased with the increasing of CoB (from 67.60 mA g(-1) to 189.35 mA g(-1)). It was indicated that CoB improved the kinetics of the hydrogenation/dehydrogenation of MgNi-type alloy. The High rate discharge capability (HRD) of the MgNi-CoB composite was higher than that of MgNi. Potentiodynamic polarization results showed that the larger corrosion resistance of MgNi alloys in an alkaline solution which benefited from the introduction of amorphous CoB. The electrochemical impedance test results showed that the values of solution resistance (R-S) and charge transfer resistance (R-1) of the MgNi-CoB alloy were reduced by CoB comparing with MgNi. In conclusion, CoB improved the electrochemical performance of the MgNi alloy significantly. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.