To improve the cyclic stability of La-Mg-Ni system alloy, as-cast La 0.75Mg 0.25Ni 3.5Co 0.2 alloy was annealed at 1123, 1223, and 1323 K for 10 h in 0.3 MPa argon. The microstructure and electrochemical performance of different annealed alloys were investigated systematically by X-Ray Diffraction (XRD). Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), and electrochemical experiments. The results obtained by XRD and SEM showed that the as-cast and annealed (1123 K) alloys had multiphase structure containing LaNi 5, (La. Mg) 2(Ni, Co) 7 and few LaNi 2 phases. When annealing temperatures approached 1223 and 1323 K, LaNi 2 phase disappeared. The annealed alloys at 1223 and 1323 K were composed of LaNi 5, (La, Mg) 2(Ni, Co) 7 and (La, Mg)(Ni, Co) 3 phases. With increasing annealing temperature, the maximum discharge capacity of the alloy decreased monotonously, but the cyclic stability was improved owing to structure homogeneity and grain growth after annealing, as well as the enhancement of anti-oxidation/corrosion ability and the suppression of pulverization during cycling in KOH electrolyte.