High epitaxial quality BaTiO3 films were deposited on the MgO (001) substrate using RF magnetron sputtering at 800 A degrees C by manipulating processing parameters. The BaTiO3 films have a similar to 200 nm thickness with a very low surface roughness but a rough interface structure with respect to the substrate. The epitaxial BaTiO3 films have a tetragonal crystal structure (a = 4.02 and c = 4.11 ) with a tetragonality (c/a) of 1.02. The c-axis of the film is parallel to the growth direction as characterized by X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy. The orientation relationship between the film and the MgO is (001)(BTO)//(001)(MgO) and aOE (c) 100 >(BTO)//aOE (c) 100 >(MgO). Epitaxial nanodomains were formed in the film with a size ranging from 3 to 20 nm. The formation of the nanodomains is associated with the rough film/substrate interface due to the modification of the substrate surface characteristics (steps, terraces, and kinks) during the process. The two-dimensional interface structure between the film and the substrate was studied and its influence on the film microstructure is discussed.