The endurance of a control and instrumentation systems in Nuclear Power Plant (NPP) is generally decided through the behaviour of the dielectric material used. The Cable Insulation Materials (CIM) should retain their remarkable qualities during their entire operating life in NPP. The CIM will be exposed to gamma irradiation at their operating environment. The short time accelerated testing has been carried out in order to anticipate the long-term operating behaviour of the CIM. Silicone Rubber (SIR) and Ethylene Propylene Diene Monomer (EPDM) are widely used polymeric materials due to their salient properties. The blending of these two polymers may result in the upgrading of their properties. The blends with varying proportions of SIR/EPDM (A-90/10; B-70/30; C-50/50; D-30/70; E 10/90) were prepared. The present investigation is directed towards the identification of the suitable composition of SIR-EPDM blend for nuclear environments. Hence, the blends were exposed to varying doses of gamma irradiation (250 kGy, 1000 kGy, 2000 kGy and 2500 kGy). The main dielectric parameters such as Breakdown Voltage (BDV), Dielectric Strength (DS), Dielectric Constant (DC) and Dissipation Factor (DF) of the un-irradiated and gamma irradiated samples were measured as per ASTM/IEC standards. It is observed that the 50/50, 30/70 and 10/90 are found to have superior dielectric performance while compared with 90/10 and 70/30 after the gamma exposure. © School of Engineering, Taylor’s University.