Upon temperature increase the Tafel dependence of the evolution of oxygen on a PbO2 layer formed anodically on Pb shifts toward higher curents. The dependence of the activation energy of the elementary processes involved in the oxygen evolution reaction on electrode potential is determined from Arrhenius curves. Upon increase in potential the activation energy increases, passing through a maximum, and decreases thereafter. This change in activation energy is explained by the mechanism of the elementary processes of the oxygen evolution reaction in which the hydrated layer of the lead dioxide is also involved.