The kinetics of the hydrogen evolution reaction in stoichiometric and non-stoichiometric hydrogen storage alloys with compositions 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) were investigated by measuring the overvoltage decay immediately after the interruption of an applied cathodic current. The total overvoltage eta for hydrogen evolution was divided into two components (eta(1) and eta(2)) corresponding to the elementary reactions. The mechanism of the hydrogen evolution reaction was analyzed on the basis of the dependence of eta(1) and eta 2 on current density. The effect of the stoichiometric ratio on the performance of the alloys as a negative electrode material in nickel-hydrogen batteries was discussed from the standpoint of relative velocity of the elementary reactions.