In this study, BaTiO3 thin films were grown by RF-magnetron sputtering, and the effects of a postannealing process on the structural characteristics of the BaTiO3 thin films were investigated. For the crystallization of the grown thin films, post-annealing was carried out in air at an annealing temperature that varied from 500-1000oC. XRD results showed that the highest crystal quality was obtained from the samples annealed at 600-700oC. From the SEM analysis, no crystal grains were observed after annealing at temperatures ranging from 500 to 600oC; and 80 nm grains were obtained at 700oC. The surface roughness of the BaTiO3 thin films from AFM measurements and the crystal quality from Raman analysis also showed that the optimum annealing temperature was 700oC. XPS results demonstrated that the binding energy of each element of the thin-film-type BaTiO3 in this study shifted with the annealing temperature. Additionally, a Tirich phenomenon was observed for samples annealed at 1000oC. Depth-profiling analysis through a GDS (glow discharge spectrometer) showed that a stoichiometric composition could be obtained when the annealing temperature was in the range of 500 to 700oC. All of the results obtained in this study clearly demonstrate that an annealing temperature of 700oC results in optimal structural properties of BaTiO3 thin films in terms of their crystal quality, surface roughness, and composition.