In-plane orientation and annealing behavior of Rutile TiO2 films grown on MgO (100) substrates by means of inductively coupled plasma-assisted sputtering were investigated. We deposited TiO2 films on relatively low temperature (≦400°C) MgO substrates in Ar–O2 mixture gases. Several films were annealed in atmospheric O2 at 800°C for 60 min. X-ray φ scan measurements and AFM images revealed that rutile TiO2 film grows on MgO (100) substrate with two orientations of TiO2 (110)[001]∥MgO (100)[011] and TiO2 (110)[001]∥MgO (100)[011]. Post annealing in atmospheric O2 at 800°C improved the crystalline preference of TiO2 film, however, formation of MgTiO3 interface layer was clearly shown by cross sectional TEM image and XPS depth analysis. Values of refractive index and band gap energy were evaluated from optical characteristics of the films. High refractive index of 2.65 at wavelength of 500 nm in as-deposited TiO2 film degraded to 2.0 in annealed film due to the formation of MgTiO3 interface layer. Through this study, we offer stable rutile (110) surface and a formation route of MgTiO3 dielectric layer.