Purpose : This study is to predict the changes of the distal segment by investing the resorption of the excessive distal segment regarding the amount of setback after BSSRO. Material and Methods : 20 patients with Mandible prognathism treated by Obwegeser-Dal Pont method during the years 2000 to 2002 were selected for this study. Group A consisted of 5 males & 5 females with a setback amount of 10mm and above(Mean $10.80mm{pm}1.03$, n=20) and Group B consisted of 2 males & 8 females with a setback amount of below 10mm.(Mean $6.10mm{pm}1.10$, n=20) Panorama X-ray was taken at day 1, 1month, 3months, 6months, and 12months after the surgery. Resorption areas of excessive distal segment were measured on these panorama X-rays and compared. Results : There was bone resorption in both groups. Group A showed more bone resorption than Group B. Group B showed slightly higher resorption rate than Group A. However, there was no statistically significant difference between the resorption rates of Group A and Group B. (P>0.05). Conclusion : More bone resorption occurred with a larger amount of setback and about one third of the excessive distal segment underwent resorption, irrespective of the amount of setback.