After thyroid surgery, the complications are infection, hemorrhage, hormonal problem, and laryngeal nerve injury. The voice alternation after thyroidectomy is usually due to the injury of the superior or recurrent laryngeal nerve. But, some patients complain the voice change without laryngeal nerve injury after thyroidectomy. This voice dysfunction may also be associated with laryngeal fixation by the impairment of vertical laryngeal movement or by vocal fold or arytenoid trauma from intubation. The drastic change in voice from the inadvertent alternation of the laryngeal skeleton during thyroidectomy has not been reported previously in English literature. In this study, the voice function was phonetically evaluated before and after thyroidectomy in 48 patients, while there was normal function of the recurrent laryngeal nerve. The acoustic and electromyographic study were performed. By the results, typical voice symptoms after surgert were easy fatigue during phonation, difficulty of high pitch and signing voice. On the acoustic analysis, the speaking fundamental frequency(SF0), range of SF0 and highest musical scale were significantly diminished after surgery. We suggest that the cause is not seen in a neural lesion, but in a disturbance of the prelaryngeal musculature. This voice changes emphasize the importance of the extralaryngeal skeleton for pitch control and early intensive speech therapy, especially in patients who need their voice professionally.