The fracture toughness of filled rubber compounds is strongly dependent on the capability both of the filler/rubber network to orient and of the rubber matrix to crystallize under straining and on the possibility that not catastrophic dissipative deformation mechanisms take place when the rubber compound is largely deformed. All these phenomena may become time dependent due to the presence of low mobility rubber originating from the interactions between polymer chains and filler particles. The dependence of the fracture behavior of carbon black filled natural rubber compounds on temperature and displacement rate was evaluated. The role of the complex structure of such compounds has been evidenced by comparing the facture behavior of pristine and previously strained compounds.