Epoxy MgO nanocomposites exhibit high surface discharge inception voltage (SDIV) in SF6 gas ambience. Increase in SDIV is observed with 3wt% of MgO-added epoxy nanocomposites, especially when the SF6 ambient gas pressure is high. Impact of thermal ageing of epoxy nanocomposites on SDIV is minimum. Dielectric response studies were carried out experimentally and compared with modelling studies. The surface potential decay and charge trap characteristics of epoxy nanocomposites vary with percentage of nano filler. Thermal aging of epoxy nanocomposites has less influence on surface potential decay characteristics for 1 and 3 wt% MgO-added epoxy nanocomposites, indicating anti-thermal aging characteristics. Surface discharge activity generates UHF with its dominant frequency at around 1 GHz. The UHF signal magnitude formed due to SD activity is minimum with 3 wt% MgO-added epoxy nanocomposites. Laser-induced breakdown spectroscopy (LIBS) studies indicate that plasma temperature and threshold fluence increases with increase in wt% of MgO in epoxy resin. Tensile and flexural properties are greatly improved for nanocomposite compared to epoxy. The dynamic mechanical analysis (DMA) indicates increased storage modulus and reduction of tan δ with epoxy nanocomposites. The glass transition temperature (Tg) and activation energy increases with wt % of nano filler. © The Institution of Engineering and Technology 2019