Obstructive sleep apnea (OSA), a breathing disorder characterized by repetitive collapse of the pharyngeal airway during sleep, can cause intermittent hypoxemia and frequent arousal. Many studies have demonstrated that the deformation of tongue base plays an important role in OSA. Currently, several medical imaging modalities have been used to record the airway changes, such as cine MRI and ultrafast CT. However, most of them are difficult to be used widely in clinical diagnosis for continuous recording the deformation of tongue in real-time, particularly during sleeping. In order to overcome these problems, a wearable ultrasonic device was developed for real-time monitor of the dynamic change of the tongue base in this study. The device includes a custom-designed 3.5-MHz ultrasonic array transducer, an ultrasound pulser/receiver, high-speed analog-to-digital converter, high speed digital I/O, and a FPGA board. The ultrasound pulse repetition frequency and pulse center frequency were controlled by the programmable FPGA board. The anthropometric measurement was carried out for verifying the system performance. Results demonstrated that the dynamic variation of tongue base can be clearly distinguished by using this wearable ultrasound.