In this study, the thermal conductivity and viscosity of TiO2 nanoparticles in deionized water were investigated up to a volume fraction of 3% of particles. The nanofluid was prepared by dispersing TiO2 nanoparticles in deionized water by using ultrasonic equipment. The mean diameter of TiO2 nanoparticles was 21 nm. While the thermal conductivity of nanofluids has been measured in general using conventional techniques such as the transient hot-wire method, this work presents the application of the 3 omega method for measuring the thermal conductivity. The 3 omega method was validated by measuring the thermal conductivity of pure fluids (water, methanol, ethanol, and ethylene glycol), yielding accurate values within 2%. Following this validation, the effective thermal conductivity of TiO2 nanoparticles in deionized water was measured at temperatures of 13 A degrees C, 23 A degrees C, 40 A degrees C, and 55 A degrees C. The experimental results showed that the thermal conductivity increases with an increase of particle volume fraction, and the enhancement was observed to be 7.4% over the base fluid for a nanofluid with 3% volume fraction of TiO2 nanoparticles at 13 A degrees C. The increase in viscosity with the increase of particle volume fraction was much more than predicted by the Einstein model. From this research, it seems that the increase in the nanofluid viscosity is larger than the enhancement in the thermal conductivity.