Due to recent developments in insulation technology extensive knowledge of the impact of small voids on the dielectric behaviour and lifetime of the insulating system is required. Our objective is to investigate the PD behaviour of epoxy resin specimens with embedded artificial micro voids in order to determine the degradation mechanisms of insulating materials due to air filled micro voids. Therefore we carried out experiments, where a set of cylindrical test specimens were positioned in an oil vessel between metal electrodes. Whilst applying high electric field strength (up to 15 kV/mm) we determined the electrical partial discharge inception at different temperatures by heating the oil vessel (22 to 85 °C). Besides the partial discharge inception and extinction voltage, the level and rate of PD inception and extinction were also monitored. We found that PD inception took place at a lower voltage level or field strength respectively for specimens with hollow glass microspheres than for specimens of pure resin. Furthermore we recognised different PD patterns for specimen with and without microspheres respectively. The impact of temperature on the PD behaviour of the tested specimens can be described as marginal for temperatures between room temperature and about 50 °C but differs for higher temperatures. The influence of temperature seems to correlate with the properties of the epoxy resin used.