In this study, we have shown that atomic force microscopy is a powerful technique to study the fractal parameters of TiO2/WO3 coatings prepared by plasma electrolytic oxidation (PEO) process. Since the surface roughness of obtained oxide coatings affects their physical properties, an accurate description of roughness parameters is highly desirable. The surface roughness, described by root mean squared and arithmetic average values, is analyzed considering the scans of a series of atomic force micrographs. The results show that the oxide coatings exhibit lower surface roughness in initial stage of PEO process. Also, the surfaces of TiO2/WO3 coatings exhibit fractal behavior. Positive correlation between the fractal dimension and surface roughness of the surfaces of TiO2/WO3 coatings in initial stage of PEO process was found. (C) 2013 Elsevier B.V. All rights reserved.