The effects of heat treatment on the electrochemical properties and structure of La0.7Mg0.3Ni2.8Co0.5 hydrogen storage alloy were studied. It is found, by electrochemical studies, that the discharge capacity, cycle stability, high rate dischargeability (HRD), exchange current density I0 and the limiting current density IL of the alloy electrodes increase after annealing treatment. The discharge capacity of the alloy annealed at 1 123 K and the cycle life of the alloy annealed at 1 223 K are the highest and the best, respectively. In addition, the exchange current density I0 and the limiting current density IL of the alloy electrode increase with annealing at 1 123 K and then decrease with increasing annealing temperature. Meanwhile, the improvement of the high rate dischargeability (HRD) of the annealing samples is consistent with the variation of the exchange current density I0 and the limiting current density IL. Furthermore, it is found, by XRD analysis, that the peak positions and peak intensities change with increasing annealing temperature, which can be ascribed to the structural change and more homogeneous composition after annealing treatment.