High-quality thin films of BaTiO3 and SrTiO3 on SrTiO3 substrate were obtained by shutting off the oxygen supply during growth. Epitaxial growths were carried out with molecular-beam epitaxy (MBE) under extremely low oxygen partial pressure (pO2 < 1×10−8 Pa). Although only Ba(Sr) and Ti metals were supplied without introducing oxidant during the growth, clear reflection high-energy electron diffraction (RHEED) intensity oscillations from layer-by-layer growth were observed. The deposited films were found to have approximately stoichiometric compositions of BaTiO3 and SrTiO3. Oxygen was automatically fed from the substrate during the growths. It was found that the BaTiO3/SrTiO3 interface was abrupt without intermixing, despite a considerable amount of oxygen seems to have moved from the substrate to the film through the interface.