Nanofillers of type carbon nanotubes (CNTs) were investigated as reinforcing agents in silicone rubber matrix. Two types of CNT, namely, single-wall CNTs (SWCNTs) and multiwall CNTs (MWCNTs), were tested as reinforcing agents in rubber matrix. These CNTs were characterized with different purity, morphology, and sonication treatment (MWCNTs). Rubber nanocomposites were prepared by mixing room temperature vulcanized (RTV) silicone rubber with CNTs. At a filler loading of 3 phr, the modulus increased by 190% for specimens with MWCNTs and 150% for specimens filled with SWCNTs. Sonication was used to de-bundle the MWCNT aggregates into individual particles and to improve filler dispersion in the rubber matrix. The resistance of the MWCNTs was almost 750 times lower than that of the SWCNTs at 3 phr. The sonicated MWCNTs (2.2 kΩ) show lower electrical resistance than the pristine MWCNTs (3 kΩ) at 2 phr. These improvements could be useful for new devices such as flexible electrodes or actuators.