An electrochemical atomic force microscope (EC-AFM) was used to study the reaction of a lead electrode in sulfuric acid electrolyte, when the reaction corresponding to what occurs at the negative electrode of a lead-acid battery took place. At first, the AFM was applied to observation of the lead electrode during cyclic-vortammetry (CV) measurement, and was found to be useful to obtaining continuous in situ images of the surface morphology. These AFM images dynamically showed the surface morphology change during the oxidation/reduction cycle. From these observation results, it was visually confirmed that the quick deposition of lead sulfate crystals occurs after supersaturation phenomena at the oxidation peak on CV, and that the slow dissolving of the lead sulfate crystals occurs after the reduction peak. AFM images of the lead sulfate morphology after oxidation were then compared with those in a different potential sweeping rate and electrolyte concentration at CV. It was clearly found that the crystal size becomes smaller when the potential sweeping rate is fast or the electrolyte concentration is high. We also compared the difference in AFM images and SEM images that were observed on the same electrode sample. (C) 2001 Elsevier Science B.V. All rights reserved.