This study was conducted to assess the positional changes of hyoid bone following the use of activator in Angles class III malocclusion patients with functional factors. For this study, 40 Angle´s class I patients and 40 Angle´s class III patients, totally 80 subjects were used. They are all in Hellman´s dental age IIIB-IIIC ranges. In lateral cephalogram to compare Angle´s class I group and Angle´s class III group, and the positional changes of the hyoid bone before and after the use of activator in Angle´s class III malocclusion group. The results were obtained as follows; 1. Comparison of Angle´s class I group and Angle´s class III group. In comparison to Angle´s class I group, hyoid bone is more anteriorly and superiorly positioned in Angle´s class III group. The hyoid bone showed reverse inclination to the mandibular plane in Angle´s class III malocclusion group. 2. Comparison of the hyoid positional change before and after use of Activator in Angle´s class III malocclusion group. The hyoid bone is displaced posteriorly and inferiorly in vertical relationship. The hyoid bone also showed counter-clockwise rotation. 3. No statistical difference was found between after Activator use data of Angle´s class III malocclusion group and Angle´s class I group. It is concluded that the hyoid bone in Angle´s class III malocclusion group changed its position, similar to Angle´s class I malocclusion group.