The multifractal behavior of rock fi'acture surfaces is sludied taking into account fractal heterogeneity and anisotropy of surface structures. A projective covering method (PCM) is proposed and used to estimate directly the fractal dimension D[2, 3) of a fracture surface. The study indicates that the multifractal spectrum of the fracture surfaces provide much additional information on the fracture mechanism and the distribution of asperity concentration on the surface. The fracture surfaces induced in rocks under different failure mechanisms display distinct multifractal behavior.