TiO2 sol containing nano anatase crystalline grains was prepared using Ti(OC4H9)4 as a precursor in a water-excessive reaction system. The processes of hydrolytic-polymeric reactions and the structures of the products were analyzed. It was found that the -OC4H9 radicals previously linked to Ti atom in Ti (OC4H9) 4 molecular are broken, and there is no organic radicals linked to Ti atoms in the final sol. The structure of particles in the sol changes along with time from tetrahedral [TiO4] to octahedral [TiO6], with the coordination number changing from 3.14 to 5.18, accordingly. Therefore, the structure becomes closer to an anatase, which is octahedral [TiO6] with a coordination number of 6.0. Transmission electron microscope micrograph also reveals the foursquare projection shape of crystalline grains with a size of 200 nm in the sol. As the particles in the sol have a quasi anatase structure, the TiO2 sol can directly photodegrade Rhodamine B under Ultraviolet illumination with a rate of 62.35%.