Application of nanofluids as a dielectric medium has gained a great interest in recent years. However, the main challenge encountered in dielectric nanofluids is the agglomeration of nanoparticles. Preventing agglomeration is important to keep the stability of dielectric nanofluids. So, in this paper, it is aimed to develop dielectric nanofluids using functionalized TiO 2 nanoparticles. The functionalization process is done using vinyl silane as coupling agent. The preparation process includes two main steps, surface functionalization of nanoparticles and dispersion of functionalized nanoparticles in the base oil. For validation of surface modification, functionalized nanoparticles are characterized using Fourier transform infrared spectroscopy (FT-IR). Dielectric properties and breakdown strength are measured and compared for un-functionalized nanoparticles based oil, functionalized nanoparticles based oil, and pure oil.