In order to improve the electrochemical performances of La-Mg-Ni system (PuNi3-type) hydrogen storage alloy, a trace of B was added in La2Mg(Ni(0.8)5Co(0.15))(9) alloy. La2Mg(Ni0.85Co0.15)(9)B-x (x = 0, 0.05, 0.1, 0.15, 0.2) hydrogen storage alloys were prepared by casting and rapid quenching. The electrochemical charging-discharging cycling lives and microstructures of the as-cast and quenched alloys were measured and analyzed. The effects of B additive on the microstructures and cycling lives of as-cast and quenched alloys were investigated in detail. The results show that the as-cast and quenched alloys are composed of the (La, Mu)Ni-3 phase (PuNi3 structure), the LaNi5 phase and the LaNi2 phase. A trace of the Ni2B phase exists in the as-cast alloys containing B. The Ni2B phase in the alloys containing B nearly disappears after rapid quenching and the relative ratio of each phase in the alloys changes with the variety of the quenching rate. The addition of B obviously enhances the charging-discharging cycling stabilities of the as-cast and quenched alloys. When B content x increases from 0 to 0.2, the cycling lives of the as-cast and quenched at 20m/s alloys were increased from 72 to 94 cycles and from 86 to 104 cycles, respectively. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.