Lead-free K0.5Na0.5NbO3-K5.4Cu1.3Ta10O29-MnO2 (KNN-KCT-Mn) ceramics have been prepared by a conventional ceramic sintering technique. The ceramics show excellent piezoelectric properties for application in power devices, and the optimum properties measured are as follows: piezoelectric constant d(33) = 90 pC/N, planar electromechanical coupling factor k(p) = 0.40, mechanical quality factor Q(m) = 1900, remanent polarization P-r = 11.8 mu C/cm(2), coercive field E-c = 0.85 kV/mm. A Rosen-type piezoelectric transformer with a dimension of 21 mm X 6 mm X 1.2 mm was fabricated using the KNN-KCT-Mn ceramics. Properties of the piezoelectric transformer operating in the first and second modes have been characterized. For the first mode, the transformer has a maximum output power of 0.7 W with a temperature rise of 14 degrees C. For the second mode, the maximum output power of the transformer is 1.8 W with a temperature rise of 33 degrees C. KNN-KCT-Mn ceramics have shown to be a potential lead-free candidate to be used in high-voltage-low-current devices.