The purpose of this study was to find out some relationship between the positional change of mandible during treatment and the prognosis after treatment of Class III malocclusion. The patients selected for this study were successfully treated two patients, and three patients who were also successful in active treatment, but showed relapse during observation. Serial Cephalograms, photos, models, treatment record of these patients were analysed in each term of treatment and observation period. The results might be summarized as follows: The patient with swing back type in which mandible rotated posteroinferiorly during active treatment showed good dental and skeletal relationship during observation. Among the patients with Y-axis type, one who had harmonious growth between maxilla and mandible showed stable dental relationship during observation, the other who had not showed relapse. The swing back type was not changed during and after treatment but the patients who had Y-axis type were unchanged in some patients, and changed into forward type in the others. During active treatment, was lower facial height(ANS-Me) increased in all 5 patients, and in observation period the patients showing increase in lower facial height had stable occlusion but the others having decrease showed unstable dental relationship.