The carbon nano-tube/nano-alumina/natural rubber composites were prepared and the properties of the composites were investigated. The fillers were in-situ modified by silane coupling agent Si69 during the preparation of the composites. The experimental results showed the composites possessed good dynamic mechanical properties and low heat build-up in the dynamic compression test. The carbon nano-tube and nanoalumina showed a synergistic effect on improvement of the thermal conductivity of the composites. For example， with 100 phr of nano alumina， the thermal conductivity increased by 120%， and with 5 phr of carbon nanotube， it increased by 23%； but when 100 phr of nano-alumina and 5 phr of carbon nano-tube were jointly used in the composite， an increased by 155% was achieved. Overall， the thermal conductivity of the composites was quite good. For the applications in which the service life of the natural rubber product was shortened due to the increase of internal temperature， combined addition of carbon nano-tube and nano-alumina was an effective solution.
