TiO2 thin films were grown epitaxially on (1120) sapphire (α-Al2O3) at 800 °C by the MOCVD method. The TiO2 films and TiO2/Al2O3 interfaces were characterized by TEM and HREM. The observations indicate that the TiO2 films are single crystalline and have the rutile structure. A majority of the films has the epitaxial orientation relationship between the TiO2 rutile films (R) and the α-Al2O3 substrates (S): (101)R||(1120)S, while the epitaxial relationship of (100)R||(1120)s has also been observed for one film. HREM studies show that the (100) film was grown on an off-cut substrate, vicinal to (1120). Detailed atomic structures of the interfaces will be presented and discussed in terms of the growth mechanism and misfit dislocation structure.