The effects of postmetallization oxygen annealing on the electrical properties of a 25 nm thick amorphous BaSm2Ti4O12 (BSmT) thin film have been investigated. The radio frequency sputtered BSmT film was well-developed on a TiN/SiO2/Si substrate. A BSmT film that was postmetallization-annealed at 20 Torr oxygen pressure exhibited a high capacitance density of 10.5 fF/mu m(2) at 100 kHz. It still showed a high capacitance density of 9.2 fF/mu m(2) and a high Q value of 67, even at 1.0 GHz, along with a relatively high k of 30. Its leakage current density was significantly improved to 8.9 nA/cm(2) at +2.0 V, and the conduction mechanism is considered to be a Poole-Frenkel mechanism. In addition, better quadratic voltage and temperature coefficients of capacitance were obtained, which were as low as approximately 169 ppm/V-2 and 76 ppm/degrees C, respectively, at 100 kHz. Therefore, it is thought that the oxygen during the annealing process significantly improves the electrical properties of the BSmT films for high-performance metal-insulator-metal capacitors.