Epoxy resins are the most used polymeric systems when it comes to high voltage insulations. Their excellent electrical and mechanical properties in combination with the ability to withstand high thermal stress are what makes them so appreciated. During usage, partial discharges (PD) can occur in high voltage machines, e.g., generators or electric motors. They may deteriorate the insulation system. To prevent machine failures of high voltage machines and to guarantee longer operating times, it is important to know the influencing factors of PD. This study deals with the evaluation of the influencing factors of partial discharge and makes an effort to assess the partial discharge resistance (PDR) of bisphenol-A epoxy resin. Neat epoxy samples and samples loaded with SiO 2 -nanoparticles are prepared and submitted to partial discharge under different atmospheres using a method similar to the IEC 60343. After electrical aging, the specific eroded volume of the polymers is measured via a non contact surface metrology system. The determining factors of the partial discharge resistance were identified. Using SiO 2 — nanoparticles, an improvement of the chemical resistance, which has decisive influence on the partial discharge resistance, was found.