A series of experiments have been performed to investigate the structures and electrochemical properties of Mm1-xMgxNi3.35-yCoyAl0.15 alloys,where Mm denotes La-rich or Pr-rich mixed mischmetal,x = 0.1,0.2,0.3,and y = 0,0.15,0.3.The specific function of the constituent elements including rare earth elements and B-side elements was discussed.