Abstract Activation energies of anodic oxygen-producing reaction on electrode of platinum, magnetite, or natural graphite were measured in aqueous solution of n/10 NaOH under stirring by the stream of oxygen gas, at temperature from about 25° to 65°C. On platinum anode, overvoltage was measured by two methods, (i) by the ordinary method just after 30 minutes from the time of closing the electric circuit, and (ii) by the oscillographic method. The activation energy calculated herefrom was found 15.9 ±2.0 kcals. by (i) method, and 13.8 ±0.6 kcals. by (ii) method. On magnetite and natural graphite, overvoltage was measured by (iii) ordinary method at the stationary state which was obtained after a few minutes. Activation energy of the former was found to be 26.2 ±3.2 kcals., and that of the latter is not obtained. The activation energy on platinum by oscillographic method is consistent with that measured by F. P. Bowden in the aqueous solution of n/5 H2SO4, which is 13–14 kcals. after being corrected about the temperature coefficient of oxygen equilibrium potential. These facts suggest that the anodic oxygenproducing reaction on platinum proceeds through the same ratedetermining step both in acid and alkaline solutions, and the mechanism is rather different on platinum from the one on magnetite.