The polymeric insulator used in high voltage system, due to their organic nature suffers from the surface degradation under various environmental, electrical stress. When these insulators are used in marine, industrial premises, under fog, mist and dew leakage current starts to flow, it results in flashover, untimely failure of the insulators. So in order to improve its flashover performance under dry and wet conditions, work was carried out by incorporating various inorganic oxides with 0, 1, 3and 5wt% into the polymer base. These are Al2O3, CeO2, MgO, TiO2, ZnO which are synthesised in the lab using solution combustion and Sol gel methods. Their Nano size and phase conversion is ascertained with XRDE test. The lab fabricated dry, wet flashover test was developed. The composites with five different inorganic oxides are aged with environmental chamber with UV(320nm), Humidity (95%), Temperature(500c) and Electric stress(5.5kV) as per IEC 62217. The dry, wet flashover tests are conducted on virgin, aged silicone rubber composites. It was found 3wt% CeO2 has least variation in flashover under both the conditions. The good bonding between Nano fillers and silicone base has paved the way for depolymerisation, regulations of the energy gains of the free carriers and enhancement of water resistance capability of the composites. This makes Nano filled Ceric Oxide Silicone rubber one of the attractive alternative for high voltage insulation system.