Ti-rich BaO–TiO 2 thin films were grown on a Pt/Ti/SiO 2 /Si substrate using rf sputtering and the structural and dielectric properties of the films were investigated. For the film grown at room temperature and rapidly thermal annealed (RTA) at 900°C for 3min, an amorphous phase with a small BaTi 5 O 13 crystalline phase was formed. As the growth temperature increased, the amount of the BaTi 5 O 11 crystalline phase increased. For the film grown at 350°C and RTA at 900°C for 3min, the homogeneous BaTi 5 O 11 phase was formed. The BaTi 4 O 9 phase was developed when the growth temperature exceeded 450°C. The thin film with the homogeneous BaTi 4 O 9 phase was obtained when the film was grown at 550°C and RTA at 900°C for 3min. The dielectric properties of the films were measured at 1–6GHz range. The dielectric constant (ϵ r ) of the BaTi 5 O 11 film was about 33 and the dissipation factor was about 0.01. The ϵ r and the dissipation factor of the BaTi 4 O 9 film were about 37 and 0.005, respectively.