Automobile industries were grown rapidly by adopting pneumatic tires. Through car performance enhancement, most tire manufacturers make an effort to improve the tire performance. Of course key point of driving is the safety of vehicle, the tire manufacturers are researching to make up the biggest fault that is a puncture. When punctured, stress would be concentrated on sidewall of the tire and heat was generated due to repetitive flexing of tire sidewall. It is accelerated by high-speed driving and lead to destruction of the tire. An accident by puncture can grow up more severe situation than a normal accident. To prevent the accident, run-flat tire has begun to be developed early in 2000. Particularly, self-supporting run-flat tire can run by maintaining the rigidity of tire with puncture. The purpose of this study is evaluation of the effect of carbon fiber (CF) and carbon nanotube (CNT) on carbon black filled natural rubber/polybutadiene compound for sidewall insert compound of run-flat tire. The CF, CNT and syndiotactic 1,2-polybutadiene particles were used as additive fillers to bring on the mechanical and dynamic properties of the compound. As a result, CNT-filled compound is superior to CF-filled system on the mechanical properties such as hardness and modulus. In contrast, CF-filled compounds showed lower hysteresis. Also, the modulus and tan ä at 60°C were increased by feeding gradually more CF. Tan ä at 60°C is representative of rolling resistance of the tire and lower heat build-up can reduce the possibility of deformation of the run-flat tire. The high aspect ratio of additive fillers, especially CNT, can improve the modulus, but deteriorate the dynamic properties. CF is more proper candidate material as extra reinforcing filler to reduce the heat generation than CNT.