<b>Measurement of pH of the Three Nano Fluid and Development of New Correlations</b> In this study the pH levels of aluminium oxide Al2O3 , silicon dioxide SiO2 , and zinc oxide ZnO nanoparticles dispersed in propylene glycol and water mixture were measured in the temperature range of 00C to 90 C. The volumetric concentration of nanoparticles in these fluids ranged from 0 to 10 for different Nano fluids. The average particle sizes APS considered was from 10 nm to 70 nm. The pH measuring apparatus and the measurement procedure were validated by measuring the pH of a calibration fluid, whose properties are known accurately. The measured pH values agreed within less than ±0.5 with the published data reported by the manufacturer. Following the validation, the pH values of different Nano fluids were measured. The measurements showed that pH of Nano fluids decreased with an increase in temperature and increased with an increase in particle volumetric concentration. For the same Nano fluid at a fixed volumetric concentration, the pH was found to be higher for larger particle sizes. From the experimental data, empirical models were developed for three Nano fluids to express the pH as functions of temperature, volumetric concentration, and the size of the nanoparticles. Nano fluids, average particle sizes APS , SiO2, Al2O3, ZnO 1263-1272 Issue-6 Volume-2 M. Raniammal