Purpose : The purpose of this study was to analyze the lower third facial changes in frontal view after mandibular setback surgery. Materials and Methods : In this study, fifteen subjects(6 males and 9 females) with class III dental and skeletal malocclusions who were treated with BSSRO(Bilateral Sagittal Split Ramus Ostetomy) were used. Frontal cephalometric radiographs were taken preoperatively and more than 6 months postoperatively, and hard tissue(H2-Hl) and soft tissue changes (S2-S1) were measured on vertical and horizontal reference lines. In 15 cases, changes which developed more than 6 months after surgery were studied. Results : The results were as follows. 1. In the facial height, hard tissue $decreased(2.46{pm}2.76mm)$ with statistical significance(P<0.01), and soft tissue also $decreased(1.64{pm}3.66mm)$. As a result, the facial height generally becomes shorter after sagittal split ramus osteotomy. 2. In the mandibular width, hard tissue $decreased(2.08{pm}3.59mm)$ with statistical sgnificance(P<0.05), but soft tissue $increased (2.14{pm}5.73mm)$ without statistically significant difference(P>0.05) postoperatively. 3. In the facial index, hard tissue $decreased(0.23{pm}2.21%)$, but soft tissue $increased(2.41{pm}3.46%)$ with statistical significance. Conclusion : One of the main purpose of orthognathic surgery is to achieve facial esthetics and harmony. In order to fullfill this purpose, it is important to carry out a precise presurgical treatment planning by estimating the changes of frontal profile after surgery.