Micromachining technologies have been developed to enhance functionality in limited space and to save materials and energy. Micro-electrical discharge machining (EDM) is one of the micro processing methods. The machining efficiency, however, decreases as hole depth increases because the discharge phenomena become unstable owing to sludge stagnation. In this paper, we propose a new EDM method that applies ultrasonic vibration in machining fluid. Cavitation generated in a hole does not only break down air bubbles in EDM but also quickens the sludge removal. The EDM characteristics in terms of parameters such as machining rate, aspect ratio, and hole appearance are investigated in comparison with those of conventional EDM. The machining rate and aspect ratio rise by a factor of about 2 and the electrode wear ratio is about 2/3 the conventional value in the micro-EDM of sintered carbide.