Roughness profiles of fracture surfaces formed as a result of the fast crack propagation through a filled rubber were analyzed by means of the height-height correlation functions. The fracture surface was found to be anisotropic in a certain domain of values of length scales; i.e., different values of roughness exponents are observed across and along the crack propagation direction. A two-dimensional analysis reveals a Family-Vicsek scaling in this domain characterized as well by two exponents. These characteristic values of the roughness exponents are found to be close to those observed for fracture surfaces of certain nonrubber materials at length scales smaller than the size of the fracture process zone. Hence, a ductile fracture process can be surmised to occur within the domain of the corresponding length scales.