Surface structure changes during redox reactions of a lead electrode and the atomic arrangement of the electrochemically formed PbSO4 crystal in H2SO4 solution were investigated by using electrochemical atomic force microscopy (ECAFM) under potential control. When the potential of the lead electrode was swept from -0.58 V vs Ag/AgCl to more positive potentials in 0.05 M H2SO4 solution, a large anodic current flowed and the electrode surface became flat and soft. This result suggests that a thick layer of fine PbSO4 crystals was formed on the electrode as a result of the dissolution-precipitation process. When the electrode potential became more positive than +1.5 V, PbSO4 was oxidized to PbO2 and clusters with sizes of about 100 nm were formed on the flat surface. The electrochemical reduction of the PbO2 resulted in the formation of large PbSO4 crystals whose sizes were more than 1 mu m. The PbSO4 crystals had atomically flat terraces with step lines which were parallel to each other. An atomically resolved image of the PbSO4 crystal was obtained on the flat terraces. The large PbSO4 crystals collapsed to 100 nm sized PbO2 clusters upon electrochemical oxidation, and this cycle was able to be repeated for many times.