BaTiO3 thin films were prepared by using metal organic acid salts on MgO(100) substrates, which have large lattice-misfit with BaTiO3. Amorphous films prefired at 470 degrees C were crystallized to BaTiO3 phase by heat treatment at higher temperature. Crystallinity and in-plane alignment of the prepared films were found to depend on the heat-treatment conditions. BaTiO3 films with high cystallinity but poor (100)-orientation were obtained in air at higher than 1200 degrees C. Whereas, (100)-oriented epitaxial BaTiO3 film was fabricated by annealing at 900 degrees C under low oxygen partial pressure (p(O-2)). Low carbon dioxide partial pressure (p(CO2)) is also found to be essential for preparation of epitaxial BaTiO3 films on MgO substrates by using metal organic acid salts.