The solidification behaviors of titania(TiO2)-water nanofluid and deionized water (DI water) were investigated using differential scanning calorimetry (DSC) at cooling rates of 1.5—9.0 °C/min. The nanofluid with 0.3 wt% TiO2 nanoparticles was prepared by dispersing the nanoparticles into DI water. The dispersion and stability was confirmed by a particle size and zeta potential analyzer. Experimental results show that the solidification temperature of the TiO2-water nanofluid was higher than that of DI water at the same cooling rate. The contact angles of TiO2 and the interior surface of the sample holder were measured, and the free energy barriers (FEB) of nucleation of the TiO2-water nanofluid and DI water were calculated. It was found that the FEB of nucleation induced by the TiO2 nanoparticles was lower than that by the flat surface, resulting in lower supercooling degree.