Anodic polarization curves of 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) electrodes were measured under the conditions of various initial concentrations of absorbed hydrogen (H/M), rates of potential sweep and temperatures. Anodic peak current (I-p) at the Mm(Ni3.6Mn0.4Al0.3Co0.7)(x) electrodes increased with an increase in x value. In addition, the I-p value depended linearly on initial hydrogen concentration and square root of potential sweep rate irrespective of, : value. Furthermore, the activation energy for hydrogen diffusion decreased with an increase in x value. From these results, it is considered that the hydrogen diffusion in the Mm(Ni3.6Mn0.4Al0.3Co0.7)(x) alloys and the electrocatalytic activity at their surfaces influence the I-p value and that they are important factors for improving the charge-discharge performance of negative electrode.