The structure of a 50-nm-thick TiO2 film grown on MgO(001) substrate maintained at 630 degrees C was studied by x-ray diffraction. Each film was fabricated by varying both the deposition rate of Ti atoms, which are produced by Ar-ion beam sputtering onto a Ti target, and the partial pressure of O-2 gas (P-O2). When Ti atoms are supplied at a rate of 0.1 nm min(-1) (4.0 x 10(14) cm(-2) min(-1)) at P-O2 = 1.1 x 10(-2) Pa, the TiO2 film exhibited the anatase structure whose (200) plane was parallel to the MgO(001). The TiO2 film with the rutile structure whose (110) plane was parallel to the MgO(001) was grown at the same deposition rate and P-O2 = 3.1 x 10(-3) Pa. Evidence demonstrating that the structure of TiO2 film is controlled only when Ti atoms and O-2 molecules are supplied simultaneously is presented.