BaTi4O9 thin films were grown on a Pt/Ti/SiO2/Si substrate using rf magnetron sputtering and the structure of the thin films were then investigated. For the films grown at low temperature (≤ 350° C), an amorphous phase was formed during the deposition, which then changed to the BaTi5O11 phase when the anneating was conducted below 950° C. However, when the annealing temperature was higher than 950° C, a BaTi4O9 phase was formed. On the contrary, for the films grown at high temperature (> 450° C), small BaTi4O9 grains were formed during the deposition, which grew during the annealing. The homogeneous BaTi4O9 thin films were successfully grown on Pt/Ti/SiO2/Si substrate when they were deposited at 550° C and subsequently rapid thermal annealed at 900° C for 3 min.