This research measured the dielectric properties of silicone rubber with various hardness in 100 Hz~3 MHz, $30{sim}170^{circ}C$ conditions. When the hardness increases from 65 degree to 75 degree, the dielectric loss increased within frequency range of 100 kHz~3 MHz and was a little change in dielectric loss within temperature range of $90^{circ}C{sim}170^{circ}C$. Thermogravimetric Analysis (TGA) showed the weight change rate increased a little while heated until $800^{circ}C$. Scanning Electron Microscope (SEM) measurement showed that Aluminium Trihydroxide($AlOH_3$) which acts as a reinforcement agent reduced the size of the particles as the hardness increased.