Abstract: The microstructure of oxide films formed on zircaloy-4 tested in autoclave at 360 ℃, 18. 6 MPa is investigated by means of scanning probe microscopy (SPM). The microstructure with only slight undulation on the surface can be examined by SPM,because it has very high resolution both on horizontal and vertical directions. So that the microstructure of cracks, pores and grains in oxide films can be clearly observed. The method for the preparation of SPM specimens is simple and convenient.