In literature there are not many experimental data on diathermic oil based nanofluids because many experimental campaigns are focused on water nanofluids. Samples of nanofluids, with nanoparticles of CuO, Al2O3, ZnO and Cu, having different shapes and concentrations varying from 0.0%up to 3.0%, have been produced and their thermal conductivity has been measured by means of hot-wire technique, according to the standard ASTM D 2717-95. Measurements were carried out to investigate the effects of volume fraction, particle size of nanoparticles on the thermal conductivity of the nanofluid. The effect of temperature has been also investigated in the range 20-60 掳C. A dependence was observed on the measured parameters and the results showed that the heat transfer performance of diathermic oil enhances more than water with the same nanoparticles.