The surface roughness has an effect on many physical properties so that an accurate description of the roughness parameters is of great interest to obtain a modelisation of a surface. In this paper, we reported that AFM and X-ray scattering are powerful and complementary techniques to study the fractal parameters of a surface. The experimental values are quite in agreement with the limitations of the Sinha's model which is applicable for smooth surfaces with a root mean square roughness sigma lower than 5 nm. We also showed that these techniques are quite suitable to study the early stages of oxidation processes of Cu and Fe samples. (C)! 2001 Elsevier Science B.V. All rights reserved.