Oil‐paper composite is the main insulation system in oil‐filled transformers. In recent years, the use of nanotechnology to improve the electrical and thermal properties of transformer oil has become a field of research interest. In this paper, the electrical properties such as breakdown strength, volume resistivity, and dielectric response of nano‐filled oil‐paper insulation are evaluated. The evaluation is carried out on a double‐layer of oil‐paper composites insulation. The double‐layer samples are prepared considering different nano‐filler types. The studied nano‐filler types are Pb3O4, Al2O3, and SiO2 with average particle size 25 nm of each. For each nano‐filler type, oil‐paper samples with different concentrations (0.04, 0.06, 0.1, 0.2, and 0.4 g/L) are prepared. The effect of nano‐filler types on the breakdown strength, volume resistivity, and dielectric response of oil‐paper composites are highly evaluated. The results show that the filler types as well as filler permittivity affects the breakdown strength, volume resistivity, and dielectric response of oil‐paper composites insulation. Also, the results show that nano‐filler with high permittivity gives higher improvement in breakdown strength of Oil‐paper composite compared nano‐filler with low permittivity. Finally, the interpretation of all obtained results considering breakdown strength, volume resistivity, and dielectric response is highly reported. [ABSTRACT FROM AUTHOR]