Amorphous strontium titanate (STO) films deposited on Si substrates by magnetron sputtering at room temperature were irradiated with 2 MeV Si ions at doses of 5x10 1 6 -1.5x10 1 7 Si + /cm 2 and post-annealed at 450 o C in vacuum. The compositional and structural changes of STO films after the ion irradiation were examined by Rutherford backscattering spectrometry, scanning electron microscopy and X-ray diffraction measurements. The Sr:Ti:O ratio of the as-deposited films was found to be approximately 0.8:1:3. Ion irradiation did not affect the amount of Sr and Ti significantly and the films remained amorphous. After annealing, however, the formation of STO crystals was observed and Sr and O were slightly lost from the films. As compared to the un-irradiated STO films, the ion-irradiated ones showed significantly enhanced crystallization behaviors upon vacuum annealing.