In this study, the effects of SiO2 nanopartides presence on the thermal conductivity of ethylene glycol were examined. Samples containing nanopartides with mass fractions of 0.005, 0.01, 0.05, 0.1. 0.5, land 5% were prepared by applying two-step method. The nanofluid thermal conductivity at temperatures of 5, 25,45 and 65 degrees C was measured by KD2. It was found that at the higher temperature, adding nanopartides has a greater effect on improving thermal conductivity. Based on results, as the nanopartides mass fraction increased, the potential of nanoparticles to improve thermal conductivity reduced. Experimental measurements showed that thermal conductivity improved up to 28.34%. As the sonication time increases, the thermal conductivity improves. The effect of sonication time on thermal conductivity depends on the temperature and nanoparticle mass fraction. It was concluded that the effect of sonication time intensifies with increasing temperature and mass fraction. In the best condition, sonication time can improve the thermal conductivity up to 4.96%. (C) 2020 Elsevier B.V. All rights reserved.