The effect of lignin, which is an important additive for the negative electrode in lead-acid batteries, is studied on lead electrodes in sulfuric acid by means of potentiostatic transient measurements and in situ electrochemical atomic force microscope (EC-AFM) observations. During oxidation of the electrodes, it is confirmed that the current transition in electrolyte with 20 ppm lignin gives a broad, hill-like curve, while that in electrolyte without lignin is a sharp peak. Nevertheless, there is little difference in electrode capacity in each electrolyte throughout the whole oxidation. In electrolyte with lignin, in situ EC-AFM examination reveals a uniform deposition of lead sulfate crystals after oxidation of the electrode. These results suggest that lignin adsorbs on the electrode surface and promotes uniform diffusion of lead ions near the surface during oxidation.