Atomic force microscopy (AFM), a powerful, high-resolution imaging technique for determining the structure of surface, was used to examine the growth of the oxide film formed on 304 stainless steel in dilute sulfuric acid solution by using alternating voltage (AV) passivation. Transmission electron microscopy (TEM) was also used to investigate the growth of the film. It was pointed out that there were pores in the film during AV passivation, causing the oxide to grow rapidly. The site of pores changes continuously with the change of the morphology of the substrate caused by active dissolution under lower potential part of square wave electric field (E-L), this make the substrate dissolved to a polishing interface during AV passivation. (C) 2002 Elsevier Science B.V All rights reserved.