In this work natural convection heat transfer of Fe 3 O 4 /Ethylene Glycol nanofluid from a horizontal heated wire in the presence of electric field was studied experimentally. Changes of Nusselt number and natural convection heat transfer coefficient in different volume fraction of nanoparticles and various field intensities were investigated. The results show that the natural convection heat transfer of nanofluid with low concentrations of nanoparticles increase compared to base fluid. Maximum natural convection heat transfer coefficient was in 0.02% volume fraction. But there is a systematic decrease in the natural convection heat transfer coefficient in high concentration of Fe 3 O 4 nanoparticles. Electrohydrodynamic increased the natural convection heat transfer of nanofluid so that heat transfer coefficient of different concentration of nanofluids was more than the ones in the absence of electric field. It was found that the highest value of natural convection heat transfer occurs in an optimum concentration and electric field intensity at 0.02% and 12.5 kV, respectively. KEY WORD : natural convection, enhancement of heat transfer, nanofluid, electrohydrodynamic