Effect of stoichiometric ratio on the electrochemical properties of negative electrodes was investigated for alloys with composition Mm(Ni3.6Mn0.4Al0.3Co0.7)(x) (Mm = misch metal, 0.88 less than or equal to x less than or equal to 1.12). The discharge capacity at a current density of 0.2 A g(-1) increased with an increase in unit cell volume of the alloys in the range of x = 0.96-1.12. The discharge efficiency increased with increasing x value, and was about 85.2% even at a high current density of ca 2 A g(-1) in the case of x = 1.12. The improved high-rate dischargeability was explained on the basis of high diffusibility of hydrogen in the bulk of alloys as the result of the relatively low stability of the hydride, in addition to the high electrocatalytic activity for the hydrogen electrode reactions of the negative electrode.