Polystyrene (PS) thin film modified with a novel ultrasonic scratching method has been studied using an atomic force microscope (AFM). Ultrasonic scratching can be realized by a combination of an AFM and a quartz crystal resonator (QCR). The PS thin film was deposited on the surface of an AT-cut QCR which oscillates with mechanical shear deformation at its resonant frequency (6.5 MHz) with amplitude of a few nm. The oscillating surface is scratched with the AFM＇s diamond tip to generate an effective cutting force. Scratching without a QCR oscillation forms bumps on the PS surface, which is known well to be a unique phenomenon of scratched polymer surfaces. However, ultrasonic scratching can result in the carving of PS thin films without the formation of bumps. The depressed bottom carved by ultrasonic scratching is fiat in comparison with that scratched without surface oscillations. Furthermore, on the previously modified area of ultrasonic scratching, bumps are not formed, even after overlapping of the scratching without surface oscillations.