PURPOSE: To evaluate the results of surgical method using plate and screws in the treatment of unstable pelvic bone fracture involving Sacroiliac Joint. MATERIALS AND METHOD: Authors reviewed 21 patients treated by surgical method from 1998 to 2002. Mean follow-up period was 15 months (12~24 month). Male were 16 and female were 5. We used plate and screws in 18 cases, just screws in 3 cases. We classified the type of fracture by Tile's classification and evaluated the results with Moon's criteria that based on reduction state in simple x-ray and patient's subjective satisfaction. RESULTS: We got the bony union in all cases. By Moon's criteria, 10 cases were good, 7 cases were fair and 4 cases were poor. In 17 cases (80.9%), we got the results over fair. Mean weight bearing exercise periods were 6.4 weeks. There were 2 infection and 2 sacroiliac arthritis after operation. CONCLUSION: As a method of surgical treatment on unstable pelvic bone fracture involving sacroiliac joint, we recommend open reduction and internal fixation with plate and screws and it may has particular advantages in early ambulation and satisfactory functional outcome.