In this experimental study, a certain amount of graphene oxide nanomaterial was dispersed in a blend of natural ester oils like coconut oil and traditionally used mineral oil to form graphene oxide nanofluids under different volume fractions. The electrical properties of the tested nanofluid samples and base oil samples, such as dielectric strength, loss tangent, and specific resistance and physical properties such as flash point and fire point, are tested as per IEC and ASTM standards. The result shows that by mixing nanoparticles with an optimum ratio of blended oils, the dielectric strength enhanced up to 68.3kV in comparison to base mineral oil and coconut oil. Loss tangent of the nanofluid sample decreased by 0.12 in comparison to coconut oil. The specific resistance of prepared nanofluid enhanced upto 4.12E11Ω-cm, which is the higher value in comparable to base coconut oil. Similarly, the flash and fire resistance enhanced up to 342°C and 370°C temperature in comparison to mineral oil and coconut oil. Thus, the tested Graphene oxide-nanofluid can be used as an alternative to mineral oil for power transformer application.