Low viscous dielectric nanofluids using a silicone oil as the base fluid and an uncured silicone elastomer as the surfactant are proposed. Two types of nanoparticles are dispersed; that is, the graphite nanopowders with a diameter of 150 nm and the multiwalled carbon nanotubes with a diameter of 30 nm and a length of over 2 mu m. The dispersion of graphite nanopowders and multiwalled carbon nanotubes in the synthesized nanofluids remains stable for a month. The enhancement factor of the thermal conductivity of nanofluids as compared to the solution without nanoparticles is found to be 3.6% for the graphite nanopowder nanofluid with the addition of a particle volume fraction of. phi = 0.1 vol% and 7.6% for the multiwalled carbon nanotube nanofluid with. phi = 0.02 vol%. Interestingly, the measured free convection heat transfer coefficient is increased by 10.4% for the graphite nanopowder nanofluid but is decreased by 5.4% for the multiwalled carbon nanotube nanofluid. On the other hand, the forced convection (measured in the fully developed laminar flow regime) is enhanced for both nanofluids, and the enhancement factor is 21.9% for the graphite nanopowder nanofluid and 14.4% for the multiwalled carbon nanotube nanofluid. The proposed dielectric nanofluids with low viscosity are expected to serve as a promising coolant for electronic devices.