The purpose of this paper is to compare the results, complication, advantages and disadvantages of treatment with closed interlocking intramedullary nail with those with plate in humeral shaft comminuted fractures. The authors have reviwed 25 cases of humeral shaft comminuted fractures, which were treated with closed interlocking intramedullary nail in 14 cases and plate in 11 cases, from November 1992 to May 1996. The results were as follows: 1. The average time of operation in closed interlocking nailing was 72 minutes and that of plate fixation was 104 minutes. 2. The average time for bone union was 14.7 weeks in closed interlocking nailing and 14.9 weeks in plate fixation. 3. The complications of closed interlocking nailing were 2 cases of delayed union, 1 case of nonunion, 1 case of postoperative radial nerve palsy and 3 cases of pain and stiffness of shoulder. 4. The complications of plate fixation were 1 case of delayed union, 2 cases of nonunion, 1 case of postoperative radial nerve palsy, 1 case of stiffness of shoulder. 5. Excellent and good functional results rated by Stewart and Hundley were 12(85%) cases in closed interlocking nailing and 8(73%) cases in plate fixation. We concluded that closed interlocking nailing is one of the better useful method of treatment in humeral shaft comminuted fractures but, the procedures should be performed exactly.