Stable magnetic nanofluids of cobalt ferrite nanoparticles were synthesized by chemical co-precipitation method. The structural, morphological and magnetic properties were characterized by the X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), and Vibrating Sample Magnetometer (VSM) respectively. The XRD study revealed the spinel structure of the prepared cobalt ferrite nanoparticles with Fd-3m space group. Prepared nanoparticles were found to be spherical in nature with average particles size of 10 nm. The prepared cobalt ferrite nanoparticles were exhibit near superparamagnetic behavior. These superparamagnetic cobalt ferrite nanoparticles used for the preparation of the magnetic nanofluids in ethylene glycol with various volume fraction concentrations viz. 0.2%, 0.4%, 0.6%, 0.8%, and 1%. The thermal conductivity of the ethylene glycol was significantly enhanced by dispersing the cobalt ferrite nanoparticles. The thermal conductivity of the prepared cobalt ferrite / ethylene glycol (COEG) magnetic nanofluid were also responded to the magnetic field intensity and shows increasing trend with increasing magnetic field intensity.