Thin films of bismuth-titanate (BiTi3O12) have been prepared by dual ion-beam sputtering. The growth process of films was observed in situ by reflection high-energy electron diffraction (RHEED). The crystalline quality of the films was characterize Rutherford backscattering (RBS) experiments. It was found that the growth of the BiTi3O12 films is influenced by a lattice mismatch between the Bi4Ti3O12 film and the substrate. Epitaxial growth of Bi4Ti3O12 films with a c-axis orientation was confirmed on LaAlO3 and SrTiO3 single crystals which have a small lattice matching condition for the Bi4Ti3O12 film. It is considered that the Bi4Ti3O12 film grows on the substrate with relaxing the lattice strain caused by the lattice mismatch as the film thickness increases.