Most of the humeral shaft fractures have been treated conservatively. If operation is indicated, most surgeons used to perform an open reduction and internal fixation with plate &Treatment of the Humeral Shaft Fracture in Adult screws. But, when open reduction and internal fixation is carried out, the periosteum and soft tissue attachments must be stripped off from the bone and operative time becomes longer. Interlocking IM nailing is an attractive procedure which does not disrupt or strip off periosteum and soft tissue at the fracture site, decrease the chance of infection and allow early exercise. Authors compare the clinical result of humerus shaft fracture which were treated by plate fixation in 25 patients and interlocking IM nailing in 16 patients who were treated at the orthopedic depaunent, Joong Ang Gil Hospital from Feb. 1992 to Jan. 1995. 1. The average time of operation in interlocking IM nail was 65 minutes and that of plate fixation was 95 minutes. 2. The average time for bone union was about 14.4 weeks in interlocking IM nail and 14.2 weeks in plate fixation. 3. The complications of interlocking IM nail were 1 case of postoperative radial nerve palsy, 1 case of delayed union, 1 case of nonunion and 3 cases of pain and stiffness of shoulder. 4. the complications of plate fixation were 1 case of infectioin, 1 case of delayed union, 3 cases of nonunion, 1 case of metal failure, 2 cases of postoperative radial nerve palsy and 2 cases of pain and stiffness of elbow. In conclusion, the interlocking IM nailing is an attractive procedure or the treatment of the humeral shaft fractures.