The new trial to apply the closed I-M nailing for 23 cases of long bone fracture has been used our department, loss of hematoma, further damage to periosteum and soft tissue were prevented; the risk of infection was reduced; and the early functional use of extremities without additional superflous external fixation could be made. The results obtained were as follows; 1. There was no case of non-union or other complication. 2. The average bone union rate was 26.1 weeks in femur, 22 weeks in tibia, or 11.5 weeks in forearm. 3. The advantages is simple method and be able to do early ambulation without following muscular atrophy or ankylosis. 4. The patients were satisfactory about cosmetic problem after operation. 5. The merits of this operation were the short hospitalization and early adaptation of social activity. 6. In conclusion, closed I-M nailing is method of choice for long bone shaft fracture when internal fixation is indicated and our operative is useful and simple.