PURPOSE: To compare the results and complications of interlocking IM nailing and plate fixation by posterior approach in the treatment of traumatic humeral shaft fracture MATERIALS AND METHODS: From March 1997 to March 2003, 49 patients undergone operation due to traumatic humeral shaft fracture. Follow-up was over one year. 28 patients operated with interlocking IM nailing initially and 21 operated with plate fixation by posterior approach prospectively. Statistics were compared using clinical and radiological outcomes and complications. RESULTS: Radiologically, bone union was observed after an average of 14.3 weeks in IM nailing, and 11.7 weeks in plate fixation. So plate fixation showed earlier bone union (p=0.012). Nonunion occurred in 4 cases (14.3%) operated with IM nailing, and 1 case (4.8%), that was open shaft fracture, with plate fixation. Nonunion occurred more frequently when operated by IM nailing. 6 cases showed limitation of shoulder movement due to damage of the rotator cuff by IM nail entry site. 1 case showed radial nerve palsy, and 1 case showed axillary nerve palsy in the case of IM nailing. Also, secondary surgery due to complications was operated in 9 cases (32.1%) in IM nailing and 1 case (4.8%) in plate fixation (p=0.03). CONCLUSION: In the case of traumatic humeral shaft fracture plate fixation by posterior approach was more useful than IM nailing in the decrease of complications and bone union. Such approach is thought to be an excellent method for anatomic reduction and nerve exploration in the case of open and comminuted fracture which accompany nerve injuries