Heteroepitaxial SrTiO3 films of perovskite structure with thicknesses of 46 to 184 nm were prepared by rf magnetron sputtering, holding substrate temperature at 400-degrees-C, on Pt films which were also epitaxially grown on a MgO(100) substrate in advance. The relative dielectric constant was estimated to be more than 300, and the leakage current density was less than 10(-8) A/cm2. The analysis of the leakage current suggests Schottky barrier formation at the interface between SrTiO3 and Pt films, with a barrier height of about 1 V.