The purpose of this study was to examine soft tissue and hardtissue changes following orthognathic surgery in patients with mandibular prognathism lateral cephalometric films were obtained immediate before surgery, 48 hours following surgery, and 6 months following surgery. 18 patients were selected (10 men, and 6 women) for this study, who had received orthognathic surgery. Statistical analysis for the each time interval differences were performed with the SPSS package. The results were as follows, ∗In the cases of mandibular sagittal split osteotomy 1. LI point was moved backward (average 7.55mm) 48 hours following surgery. 6 months later, it was returned forward (average 1.1mm) Relapse rate was 14.6%. 2. Pog was moved backward (average 8.3mm) 48 hours following surgery. The ratio of horizontal change of soft tissue to hard tissue at pog is 0.95 1 ∗In the cases of maxillary Le-Fort I osteotomy & mandibular sagittal split osteotomy. 3. A point was moved forward (average 3.31mm) 48 hours following surgery. 6 months later, it was returned backward (average 0.31). Relapse rate was 9.4% 4. 6 months later, the ratio of facial convexity angle change of soft tissue to hard tissue is 0.63 1.