This research measured the dielectric properties of silicone rubber with various hardness in 100 Hz∼3 MHz, 30∼170℃ 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℃～170℃. Thermogravimetric Analysis (TGA) showed the weight change rate increased a little while heated until 800℃. Scanning Electron Microscope (SEM) measurement showed that Aluminium Trihydroxide(AlOH3) which acts as a reinforcement agent reduced the size of the particles as the hardness increased.