In order to investigate the vibration pattern, especially the vibrational phase of tissue beneath the vocal fold mucosa, an imaging method called electroglottogram-triggered ultrasonography is proposed. The ultrasonic images of the vocal fold vibration are obtained in the coronal plane from five adult subjects during phonation. The velocity of the vocal fold tissue beneath the mucosal surface is obtained by using a motion estimation method. The results show that the vibration phase difference between tissues at different locations beneath the vocal fold mucosa results in a mechanical wave traveling upward at a speed of 720 to 1826 mm/s.