Ferroelectric b-axis oriented BaTi2O5 thin film was successfully prepared on MgO (100) substrates by laser ablation. The effects of substrate temperature (T-sub) and oxygen partial pressure (P-O2) on the crystal structure, surface morphology, and dielectric property of the film were investigated. BaTi2O5 thin films were obtained at T-sub = 923-973 K and P-O2 = vacuum to 17.5 Pa on MgO (100) substrates. The orientation of the films changed from (710) to (020) depending on T-sub and P-O2. The optimum conditions for preparing film with a dense-and elongated texture were T-sub = 973 K and P-O2 = 12.5 Pa. The permittivity of the ferroelectric b-axis oriented BaTi2O5 thin film showed a sharp peak (similar to 2000) at 750 K. (c) 2007 American Vacuum Society.