Single-phase and biphase TiO2 nanoparticles have been prepared by the sol-gel method. Our results showed with the increase of the gelatinization time and the calcination, the size of initial anatase particles and the size of final biphase particles were increased; however, distortion and agglomeration of both of TiO2 nanoparticles were decreased. Moreover, the mass fraction of rutile (MFR) phase and the activation energy of the phase transformation (PT) from anatase to rutile decrease. We demonstrated that the morphology and homogeneity of the initial anatase nanoparticle could have more important than its initial size to appear the lower activation energy.