A highly ordered grating pattern is observed in the SrRuO3 buffer layer in an SrTiO3/SrRuO3 bilayer system on (0 0 1) SrTiO3 substrate. By means of high-resolution transmission electron microscopy, the grating lines are found to consist of lattice defects and nanoscale precipitate particles. The particles are identified as pure ruthenium crystals. Correspondingly, Sr-rich Ruddlesden-Popper planar defects occur in the nearby area. This unusual film growth phenomenon may provide a novel way to fabricate ordered structures in oxide films for potential applications. (C) 2003 Elsevier Science B.V. All rights reserved.