Severe open fracture of the tibia have a high incidence of complications and a poor outcome. The most usual method of stabilization was by external fixation, but the advent of small diameter interlocking intramedullary nails has introduced a new option. From the June 1992 to December 1997, 55 cases of open tibial shaft fracture were treated with unreamed interlocking intramedullary nailing at the department of orthopedic surgery, Pusan National University Hospital. The purpose of this study is to evaluate its result and complications. Mean age was 31, mostly male. The main cause of trauma was traffic accidents(30 cases, 55%) and fracture sites consisted of mid 1/3 portion over 75%. According to the Gustilo & Anderson classification 8 type I(15%), 22 type II(40%), 15 type IIIA(27%) and 10 type IIIB(18%) were shown. Union time was 28.3 weeks on an average and union rate was 98%. There were 5 cases(9%) of delayed union, 2 cases(4%) of deep infection and 1 case(2%) of chronic osteomyelitis. In conclusion unreamed interlocking intramedullary nailing can be the first choice treatment in the treatment of open tibia shaft fractures with low postoperative infection.