Sonodynamic therapy is a new modality based on the synergistic effect of ultrasound and a chemical compound referred to as "sonosensitizer" for treatment of diseased sites such as cancer. However, by external ultrasound exposure, it is difficult to transmit ultrasound deep within the human body at adequate intensity because of transmission losses caused by the difference of specific acoustic impedance between media. Therefore, the aim of this study is to develop focused ultrasonic transducers using concave-shaped PZT for localized sonodynamic therapy in the human body. A concave-shaped PET was fabricated from a bulk PZT using a high-speed micro-milling machine, and then repolarized for the optimized polarization direction. The measurement result of the acoustic field using a PVDF hydrophone indicated that (he ultrasound emitted from the transducer was successfully focused in three-dimensions. At the focal point, the measured peak intensity would be sufficient for sonodynamic therapy.