In this study, the effects of loading levels of nano BN, nano SN and synthetic ND particles on the thermal and mechanical properties of silicone rubber were investigated. Nanoparticle-filled silicone rubber composites were prepared by cast molding process. In general, incorporation of thermally conductive nanoparticles to the silicone rubber matrix improved the thermal conductivity of the composites. BN particles have the most pronounced effect on the thermal conductivity in comparison to SN and ND particles at any given loading level. TGA studies revealed that the thermal stability of the SN/ silicone rubber system increased as the filler loading level increased; however, BN and ND facilitated the thermal degradation of the silicone rubber nanocomposites. For tensile test, it is observed that the addition of nanoparticles generally increased the tensile strength of silicone rubber composites compared to the neat silicone rubber. However, for BN system, the tensile strength of the composites decreased when more than 1.5 vol.% of BN is loaded in the system. The reduction was caused by the existence of voids and agglomerations in the BN/silicone rubber system. In general, tensile modulus and strain at break of nanocomposites increased with the incorporation of nanoparticles into silicone rubber matrix.