Abstract: Positional changes of laryngeal structures during F0 changes were measured in order to examined physiological mechanism of F0 lowering. It is widely known that F0 raising is mainly produced by the function of the cricothyroid muscle to activate the rotation between the crocoid and the thyroid cartilages. However, F0 lowering cannot be explained by the relaxation of the cricothyroid muscle, and its mechanism is still a physiological question to be examined. To this end, the present study adopted the magnetic resonance imaging (MRI) for the midsagittal plane near the larynx. The images were taken using multiple subjects during repeated sustained phonation of a vowel in F0 range of approximately 1.0-1.5 octave. Manual shape extraction was performed to measure relative positional changes of laryngeal components associated with these F0 changes. In the results, vertical movement of the larynx was observed consistently in correlation with F0 levels. Towards lower F0, the rotation of the cricoid cartilage was observed associated with laryngeal descent. This rotation to the direction of shortening the vocal fold is produced by the lowering of the posterior plate of the cricoid cartilage along the physiological curvature of the cervical vertebra. The tendency of laryngeal descent and strap muscle activity in F0 lowering can be accounted for by this mechanism.