PURPOSE: To find the factors influencing bone union in segmental tibial shaft fractures treated with interlocking intramedullary nailing, and to find the special attentions during operation based on this factors. MATERIALS AND METHODS: This retrospective study made to investigate the medical records and plain radiograms of 32 patients who treated with interlocking intramedullary nailing. We statistically analyzed the correlation between bone union time and factors influencing bone union, including fracture site, fracture pattern, Melis type, open fracture, nail diameter, reaming, postoperative gap, postoperative angulation. RESULTS: The factors that showed the significant difference statistically were fracture site, Melis type, open fracture, postoperative gap, postoperative angulation. The factors that showed no significant difference statistically were fracture pattern, nail diameter, reaming. CONCLUSION: We recommend that surgeons should be considered the site and type, open fracure in preoperative stage. During operation, try to reduce it accurately without angulation and gap if possible. And so, the careful planing of treament can be expected with a high rate of union and a low rate of complication.