Abstract: Carbon nanotubes (CNTs) can be used to improve the thermal and mechanical properties of composites because of their excellent characteristics. Methyl vinyl silicone rubber matrix composites filled with alumina (Al₂O₃) powder and CNTs were fabricated by a conventional mechanical blending method. The effects of the mass fraction of Al₂O₃ powder, surface modification of Al₂O₃ powder by silanization with dodecyltrimethoxysilane and the addition of CNTs on the thermal conductivity, Young's modulus and hardness of the composites were investigated. Results showed that a higher mass fraction of Al₂O₃ powder results in a higher thermal conductivity of the composites. When the mass fraction of Al₂O₃ powder was fixed, the thermal conductivity, Young's modulus and hardness of the composites were obviously improved by surface modification of the powder and adding a small amount of CNTs. A combination of the modified Al₂O₃ filler and CNT filler improves the interfacial interaction between the fillers and rubber matrix by the formation of better heat conduction channels and network structures in the rubber matrix, thereby improving the thermal conductivity and mechanical properties of the composites.