Effect of temperature and shear rate on appearances of extruded silica filled styrene butadiene rubber compound was investigated by capillary rheometer. It was revealed that in low shear rate region flow instability appeared as shark-skin, and the types of flow instability changed to melt fracture with increasing shear rate. The shear viscosity with Bagley correction and the extensional viscosity calculated by Cogswell’s method were also investigated. The shear viscosity with Bagley correction didn’t relate to the melt fracture occurrence. The extensional viscosity calculated by Cogswell’s method, however, got rising with increasing extensional rate, and then, shark-skin switched to melt fracture. This switching phenomenon indicates that melt fracture occurrence of rubber compound is due to strain-hardening by extensional flow in entrance of capillary die and then wall slip phenomenon also happens.