Abstract: The DC electrical resistivity-temperature characteristic is an important property for insulating materials to operate at a high stress level. In order to improve the DC electrical resistivity at elevated temperature in a targeted way, a positive temperature coefficient (PTC) material (BaTiO₃-based compound (BT60)) was selected as the filler in this paper, whose electrical resistivity has a PTC effect when the temperature exceeds its Curie temperature. The BT60 was treated with hydrogen peroxide and (3-Aminopropyl) triethoxysilane. Epoxy composites with different loadings of BT60 fillers (0 wt%, 0.5 wt%, and 2 wt% of epoxy) were prepared, denoted as EP-0, EP-0.5, and EP-2. It was shown that BT60 was able to maintain the DC breakdown strength when its loading was less than 2 wt% of epoxy. As the temperature exceeds 60 °C, BT60 will compensate for the negative temperature coefficient effect of epoxy resin to some extent. The electrical resistivity of EP-2 was improved by 55% compared with that of neat epoxy at 90 °C. It was found that the potential barrier at the grain boundary of BT60 and the deep traps in the interface between BT60 and the epoxy resin hinder the migration of carriers and thus increase the electrical resistivity of epoxy composite.