The microstructure and electrochemical hydrogen storage characteristics of La0.67Mg0.33-xCax Ni2.75Co0.25 (x = 0, 0.05, 0.10 and 0.15) alloys are investigated. The results show that all alloys mainly consist of (La, Mg)Ni-3 and LaNi5 phases, besides a small amount of (La, Mg)(2)Ni-7 phase. The cycle stability (S-80) after 80 charge/discharge cycles of all alloy electrodes first increases from 60.1% (x = 0) to 64.2% (x = 0.05), then decreases to 45.9% (x = 0.15). The high rate dischargeability of all alloy electrodes first increases from 52.6% (x = 0) to 61.4% (x = 0.10), then decreases to 57.2% (x = 0.15). Moreover, the charge-transfer resistance (12) first decreases from 168.2 m Omega (x = 0) to 125.7 m Omega (x = 0.10), then increases to 136.6 m Omega (x = 0.15). All the results indicate that the substitution of Mg with a certain amount of Ca can improve the overall electrochemical characteristics. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.