Ferroelectric BaTiO3 thin films have been fabricated on SrTiO3(001) substrate using pulsed laser deposition. In order to investigate the phase transition behavior of the thin films, we have conducted high-temperature x-ray diffraction in the process of heating and cooling. Lattice constants, degree of c-axis orientation and crystal quality of the thin films were characterized as a function of temperature. The results show that the temperature of tetragonal-to-cubic phase transition for a BaTiO3 thin film is much higher than that of BaTiO3 bulk single crystal, and the phase transition of BaTiO3 thin film occurs in a wide temperature range (from 500 to 800 °C). The tetragonal-to-cubic phase transition for BaTiO3 thin film is irreversible. © 1999 American Institute of Physics.