In this paper, the influence of heat treatment on the electrochemical properties of La0.67Mg0.33Ni2.5CO0.5 alloy electrodes has been studied. The results show that, after heat treatment, the electrochemical properties including the discharge capacity, width of discharge plateau and cyclic stability have been improved markedly. The discharge capacity of the alloy annealed at 1123 K is the highest and the cycle life of the alloy annealed at 1223 K is the longest, respectively. In addition, the exchange current density 10 and the limiting current density I-L of the alloy electrode both increase when annealed at 1123 K and then decrease when the annealing temperature increases to 1223 K. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.