Accurate determination of the thermophysical properties of nanofluids and the parameters affecting them are of particular importance in the industrialization of nanofluids. One of the most important parameters affecting properties such as viscosity and thermal conductivity is the pH of the nanofluid. In this research, the pH levels of three metal oxide nanoparticles including aluminum oxide (AL₂O₃), magnesium oxide (MgO) and zinc oxide (ZnO) dispersed in distilled water were measured in the temperature range between 303 K to 333 K and concentration range between 0.01 to 1% volumetric concentration. For more accuracy, pH measurements were performed twice for each sample and the mean value for the final pH was recorded. The results showed that with increasing the temperature by about 10%, the pH values ​​of aluminum oxide, magnesium oxide and zinc oxide nanofluids decreased by 37, 11 and 9%, respectively. Also, the addition of aluminum oxide nanoparticles has given acidic properties to distilled water, but the addition of magnesium oxide and zinc oxide nanoparticles to distilled water have given alkaline properties to the suspension. Finally, using the experimental results obtained for three metal oxide nanofluids, an equation for predicting pH as a function of concentration and temperature was proposed.