The electrochemical corrosion processes of iron in a berate solution have been investigated by in situ electrochemical atomic force microscopy (ECAFM). A freshly polished iron surface is easily passivated electrochemically in a berate solution to give a film which is different from the oxide layer which forms on the iron surface in air. Most areas of the passive film are uniform, but some defects still exist in the film which allow localized corrosion to occur. In situ ECAFM can be used to examine these defects directly and to observe the initial corrosion processes in which ferric oxide particles are both formed and reduced by cyclic voltammetry.