There is a marked difference in the growth features of Si films on Al2O3 with and without an Al pre-deposition layer. This difference is studied using coaxial impact-collision ion scattering spectrometer (CAICISS). The terminating atoms of the Al2O3 substrate surface pretreated by the Al pre-deposition layer was identified as being Al atoms combined with O atoms. The Al2O3 was grown epitaxially on Si(lll) substrate by MBE with N2O gas and an Al Knudsen cell. The Al layer was evaporated from the K-cell at a rate of 0.5 Angstrom/s onto the Al2O3 (111)/Si(111) substrate at room temperature, followed by thermal annealing at 880 degrees C for 5 min. In CAICISS measurements, 2 keV He+ was used as the primary ion, and the time of flight (TOF) spectra and dependence of the scattered He intensities on the angle of incidence angle were studied. An epitaxial Si layer with significantly improved crystalline quality and surface morphology was obtained.