This work aims to investigate the effects of carbon black (CB) and carbon nanotube (CNT) on mechanical properties and thermal behaviors of natural rubber (NR)/styrene butadiene rubber (SBR) blend at NR/SBR weight ratio of 80/20. CB loadings from 3-9 phr and CNT with 0.1-0.4 phr loadings were used as fillers in this study. The composites were prepared by latex compounding method. The specimens were examined for their tensile and dynamic mechanical properties and thermal stability using the universal testing machine, dynamic mechanical analyzer and thermal gravimetric analyzer, respectively. The tensile strength and modulus of the composites were improved as a result of the incorporation of CB and CNT. Dynamic mechanical analysis showed that the CB and CNT filled composites possessed high stiffness and low damping characteristics. Thermal stability of the composites was also proved to be better than the unfilled-rubber blend.