Abstract: Fractal characteristics of metallic worn surfaces in a sliding tribological system were investigated using structure function analysis method.It is shown that the profiles of the worn surfaces had fractal structure within the range of the length scale less than S m the fractal parameters of the surface profiles could be determined conveniently by structure function analysis.The fractal dimensions of the worn surface profiles in the direction orthogonal to sliding direction were employed as the characteristic fractal dimensions that are in close relationship with the wear rates of the alloys studied.There is an optimal fractal dimension value for a material,which corresponds to the minimum wear rate.