The purpose of this study was to evaluate the postoperative stability of the severe open bite or mandibular prognathic patients after mandibular set back surgery by Obwegeser II method. There were 19 patients who had been undergone Obwegeser II method. The horizontal and vertical position of the cephalometric points were measured preoperation and immediate postoperation, postoperative 1 month, postoperative 6 months ; were analyzed by linear measurement to evaluate changes in skeletal landmark and the relapse was compared between open bite group and prognathism group. By the operation, horizontal change of B was $6.84{pm}4.35mm$ and vertical change of B was $6.28{pm}3.25mm$ in open bite group and horizontal change of B was $14.20{pm}4.81mm$ and vertical change of B was $1.99{pm}2.66mm$ in prognathism group, horizontal change of Pog was $3.82{pm}5.71mm$ and vertical change of Pog was $5.38{pm}2.11mm$ in open bite group and horizontal change of Pog was $13.24{pm}5.99mm$ and vertical change of Pog was $1.91{pm}0.94mm$ in prognathism group. Between immediate postoperation and postoperative 1 month, all skeletal landmarks change was no statistical difference (p>0.05) and there were no statistical difference between open bite group and prognathism group except x-Me landmark (p>0.05). Between postoperative 1 month and 6 months, horizontal change of B was $0.12{pm}1.35mm$ and vertical change of B was $1.47{pm}1.48mm$ in open bite group and horizontal change of B was $1.43{pm}1.35mm$ and vertical change of B was $0.82{pm}1.99mm$ in prognathism group, horizontal change of Pog was $0.13{pm}1.40mm$ and vertical change of Pog was $0.88{pm}1.71mm$ in open bite group and horizontal change of Pog was $1.08{pm}1.74mm$ and vertical change of Pog was $0.47{pm}1.57mm$ in prognathism group (p>0.05) and there were no statistical difference between open bite group and prognathism group (p>0.05). Between immediate postoperation and postoperative 6months, horizontal change of B was $0.24{pm}1.17mm$ and vertical change of B was $1.87{pm}1.63mm$ in open bite group and horizontal change of B was $1.54{pm}1.55mm$ and vertical change of B was $1.04{pm}1.96mm$ in prognathism group, horizontal change of Pog was $0.91{pm}1.46mm$ and vertical change of Pog was $1.18{pm}2.05mm$ in open bite group and horizontal change of Pog was $0.96{pm}1.62mm$ and vertical change of Pog was $1.23{pm}2.35mm$ in prognathism group (p>0.05) and there were statistical difference between open bite group and prognathism group in x-B, x-Pog, x-Gn, x-Me (p<0.05). Obwegeser II method is considered as one of the best operation when surgical correction of severe open bite or severe mandibular prognathism is needed.