Fractal geometry is applied to the characterization of rough surfaces. The variation law of surface topography during running-in period is studied with scale-independent fractal parameters. The theoretical relation of real contact area between rough surfaces to profile fractal parameters, material properties and load, etc. is obtained. Using the relation and Rowe’s modified adhesion theory, a fractal model of running-in wear is developed. Theoretical analysis and experimental researches show that the result calculated by this wear models are consistent with the experiments. q1999 Elsevier Science S.A. All rights reserved.