PURPOSE : We evaluated the result of tibial fracture with butterfly fragment treated with interlocking intramedullary nailing and union of butterfly fragment. Material and Method : The thirty tibial fractures with butterfly fragment treated with interlocking intramedullary nailing from 1994 February to 1997 January were followed up more than 12 months. They were clastified by Henleys classification based on the size of fragment and Johner and Wruhs classification cased on the comnlinution and accident mechanism. We evaluated the bone union of tibial fracture and butterfly fragment itself. RESULTS: The time for bone union was Bl-14.5, B2-16.2, B3-18.8 weeks and Type I-15.2, Type II-17.1 Type III-18.3 weeks. In proximal and distal part of butterfly fragment, the time for bone union was 8.6 and 7.2 weeks in type I, 10.5 and 9.3 weeks in type II, and 11.8 and 10.2 weeks in type III. As the displacement of fragment were classified into 0-5, 5-10, and more than 10mm, the time for bone union was 15.3, 15.0 weeks in type I(no case in more than 10mm), 16.4, 17.5, 18.2 weeks in type II, and 17.7, 18.4, 20.3 weeks in type III. CONCLUSION : As the size and comminution of butterfly fragment increased, bony union was delayed. The union of spiral fracture in distal tibia was earlier than others, unrelated to the size of butterfly fragment. For the union of butterfly fragment, the distal part had earlier union than the proximal part. As the displacement of fragment was increased bone union was delayed.