This investigation has been carried out to study on preparation, thermal conductivity and dielectric strength of Ag- WO3 hybrid nanofluid while the base fluid was transformer oil. The reasons of selecting silver and WO3 as nanoparticles have been completely discussed. Applied nanofluids have been prepared by a one-step method known as Electrical Explosion of Wire (E.E.W). Measuring zeta potential of utilized hybrid nanofluids in three different weight fractions of 1%, 2% and 4% has been experimentally carried out. Thermal conductivity of applied nanofluids in temperature range of 40–100 °C has been measured by a KD2 pro thermal properties analyzer. The results showed that thermal conductivity of applied hybrid nanofluids increased by 41% in higher weight fraction and 100 °C. Finally, it has been observed that electrical conductivity of hybrid nanofluids decreased to 35 kV in 4% wt. Keywords: Hybrid nanofluid, Thermal conductivity, Dielectric strength, E.E.W, Transformer oil