The surface morphologies of lead dioxide layers, which were formed on a pure lead substrate and the Pb–Sb a (100ppm–3%) alloy substrate, were directly observed with the electrochemical atomic force microscope (EC-AFM) in 1.250g/cm3 sulfuric acid electrolyte and then they were analyzed with X-ray diffraction (XRD). The particle size of the lead dioxide became significantly smaller with the increase of the amount of antimony in the substrate alloy. From this result, it was considered that such small particle size serves to increase the reaction area of the positive electrode and the total electrical contact area between the positive active material (PAM) particles. Also, the interface resistance between grid and the PAM can become lower, if the density of the corrosion layer formed around the grid were to be higher for the small particles. By XRD analysis, it was found that the inter-atomic distance of the lead dioxide on the Pb–3wt.% Sb alloy substrate shrank compared to that on a pure Pb substrate.