Experimental investigations were carried out for the determination of thermal conductivity of silicon dioxide (SiO2) nanoparticles dispersed in 60% ethylene glycol and 40% water by mass. Experiments conducted in a temperature range of 20 °C to 90 °C and for several particle volumetric concentrations up to 10% showed that the ratio of thermal conductivity of nanofluid to that of the base fluid increased with an increase in temperature and volumetric concentration. As an example, as much as a 20% enhancement in thermal conductivity was evidenced for a particle volumetric concentration of 10% at 87 °C. Comparison of experimental results of this nonmetallic nanoparticles suspension with the well-known model developed by Hamilton and Crosser for microparticles suspensions, exhibits that this model underpredicts the thermal conductivity of nanofluids. Therefore, a new correlation has been derived following recent models developed for metallic nanoparticles suspensions, which is a combination of the Hamilton–Crosser model plus a term due to the Brownian motion. This new correlation expresses the thermal conductivity of silicon dioxide nanofluid as a function of temperature, volumetric concentration and the properties of the base fluid and the nanoparticles.