Sonochemical synthesis of nanostructured TiO2 has been carried out successfully at room temperature. Heat-treatments have been applied to as-prepared sample and the microstructural evolution has been studied by X-ray powder diffraction and electron microscopy (SEM, TEM and HRTEM). The results showed that particle growth process and coarsening mechanism are governed by the mobility of triple junction. Also it was observed that an agglomeration of nanoparticles promotes the growth of well-oriented crystalline twin structures. Furthermore, rutile particles are attached to the anatase particles by forming a coherent interface during the phase transformation anatase-rutile, this interface is energetically preferred nucleation site for rutile phase. Finally, the complete phase transformation to rutile is related with a reduction in the total free energy of the system. Therefore, the microstructural evolution reported herein may open new perspectives for the development of TiO2 nanoparticles as a promising material, which can be widely applied to photocatalytic system.