Single-phase potassium tantalate (KT) thin films with excellent film flatness and crystallinity have been synthesized on a tantalum substrate in 2.0 M KOH solution at 150 degrees C by a hydrothermal-electrochemical method under a galvanostatic condition. A pyrochlore structure of the thin KT films was identified by XRD pattern analysis. The films show good adherence to the substrate and the film thickness could be as much as 2 mu m. The electrical properties of the films were characterized through the determination of capacitance by electrochemical impedance spectroscopy at room temperature. Dielectric constants yielded from capacitance measurements have been calculated to have values higher than 300. The dependence of cell voltage on reaction time reflects the mechanism of film formation. The preparation conditions and morphology of the films were consistent with the proposed film formation mechanism.