When a Pb/PbO2 electrode immersed in H2SO4 solution is subjected to polarization in the lead dioxide potential region (phi >1.0 V vs. Hg/Hg2SO4 reference electrode), H2O is decomposed releasing oxygen. The aim of this investigation is to elucidate the mechanism of the reactions taking place on oxygen evolution. Linear-sweep-voltametric cycling according to various cycling programs has been performed, and the structure of the anodic layer has been examined through scanning electron micrscopy and x-ray diffraction. It has been established that at potentials in the region 1.0 1.3 V the electrode has passive behavior (i.e., only a weak current passes through it), and in the range 1.3 1.0 V and leads to the formation of OH radicals, the second takes place at phi >1.3 V. It is assumed that these reactions proceed in the hydrated PbO(OH)(2) layer of the lead dioxide. Both reactions are localized in a certain number of active centers in the hydrated PbO(OH)(2) layer. At phi <1.3 V, the products of the first electrochemical reaction block these active centers and hence the current decreases significantly. At phi >1.3 V, the second electrochemical reaction proceeds, as a result of which oxygen is evolved due to oxidation of the OH radicals and consequent unblocking of the active centers. The electrode is activated, and the reaction resistance is the dominant rate-limiting factor. The present contribution proposes a mechanism of the elementary processes that occur on oxygen evolution in light of the gel-crystal structure of the PbO2 layer. This mechanism involves the hydrated polymer chains in the gel layer.