It is known that ultrasound affects action potentials in neurons, but the underlying principles of ultrasonic neural stimulation are not clearly elucidated yet. In this study, we measured the action potentials of rat hippocampal neurons cultured on multi-electrode arrays during ultrasound stimulation. From most of electrodes, it was observed that the ultrasound stimulation increased the frequencies of action potentials (i.e., spikes) during ultrasound stimulation.