PURPOSE : this paper was to evaluate the treatment results in the viewpoint of bone union, union time, and complications including infection of unreamed nailing of pen tibial fractures. MATERIALS AND METHODS : We reviewed 46 open tibial shaft fractures that were treated with unreamed tibial nail. AO unreamed tibial nail was inserted after reduction under image intensifier control, Considering factors were severity of open wound, type and location of fractures. RESULTS : Average union time of open fractures was 21.3 weeks, nonunion rate was 2/46(4%). Average union tiome were 24.1, 19.7, 24, 24, 20 weeks in open grade I , II, IIIa, IIIb, IIIc fractures. According to the type of fractures, average union time were 20.4, 23.6, 25.7 weeks and nonunion rate were 0/22, 1/18, 1/6 in type A, B, C fractures. According to the level of fractures, average union time were 24.0, 20.0, 24.1 weeks in proximal, middle, and distal fractures. There was no signficant differences in average period of radiologic union, infection rate and nonunion rate according to fracture level, open grade, but longer union time and higher nonunion rate were observed in complex and comminuted fractures(p<0.05). CONCLUSION : With adequate soft tissue treatment, the unreamed intramedullary nailing can be a good treatment modality for open tibial shaft fractures, even to grade IIIB.