In order to improve the electrochemical performances of La-Mg-Ni based electrode alloys with PuNi3-type structure, a trace of boron was added in La0.7Mg0.3Ni2.55Co0.45 alloy. The La0.7Mg0.3Ni2.55Co0.45Bx(x=0, 0.05, 0.1, 0.15 and 0.2) alloys were prepared by casting and rapid quenching. The electrochemical performances and microstructures of the as-cast and quenched alloys were investigated. The effects of rapid quenching on the microstructures and electrochemical performances of the above alloys were investigated. The results show that the as-cast and quenched alloys are composed of (La, Mg)Ni3 phase, LaNi5 phase and LaNi2 phase. A trace of the Ni2B phase exists in the as-cast alloys containing boron, and the Ni2B phase in the B-contained alloys nearly disappears after rapid quenching. Rapid quenching increases the amount of the LaNi2 phase in the B-free alloy, but it decreases the amount of the LaNi2 phase in the boron-containing alloys. The effects of rapid quenching on the capacities of the boron-containing and boron-free alloys are different. The capacity of the B-free alloy monotonously decreases with increasing quenching rate, whereas the capacities of the B-contained alloys have a maximum value with the change of the quenching rate. The rapid quenching can improve the stability of La-Mg-Ni based electrode alloy but lowers the discharge plateau voltage and decreases the plateau length. The effect of rapid quenching on the activation capabilities of the alloys was complicated. In order to improve the electrochemical performances of La-Mg-Ni based electrode alloys with PuNi3-type structure, a trace of boron was added in La0.7Mg0.3Ni2.55Co0.45 alloy. The La0.7Mg0.3Ni2.55Co0.45Bx The effects of rapid quenching on the microstructures and electrochemical performances of (x = 0, 0.05, 0.1, 0.15 and 0.2) alloys were prepared by casting and rapid quenching. The electrochemical performances and microstructures of the as-cast and quenched alloys were investigated. the results show that the as-cast and quenched alloys are composed of (La, Mg) Ni3 phase, LaNi5 phase and LaNi2 phase. A trace of the Ni2B phase exists in the as-cast alloys containing boron, and the Ni2B phase in the B-contained alloys near disappears after rapid quenching. Rapid quenching increases the amount of the LaNi2 phase in the B-free alloy, but it decreases the amount of the LaNi2 phase in the boron-containing alloys. of rapid quenching on the capacitie s of the boron-containing and boron-free alloys are different. The capacity of the B-free alloy monotonously decreases with increasing quenching rate, while the capacities of the B-contained alloys have a maximum value with the change of the quenching rate. The rapid quenching can improve the stability of La-Mg-Ni based electrode alloy but lowers the discharge plateau voltage and decreases the plateau length. The effect of rapid quenching on the activation capabilities of the alloys was complicated.