Plaster of Paris is an effective ancillary treatment in the surgery of infected cavities in bone. It is well tolerated and spontaneously absorbed over the period of weeks to months, being replaced by bone of normal architecture. When the antibiotics incorporated into plaster of Paris, the antibiotics are capable of prolonged local release in bactericidal concentrations. Therefore it is proposed that antibiotics loaded plaster of Paris might be a simple adjuvant technique after good surgical debridement for the treatment of bone infection. The authors carried out an experiment to study the effect of plaster of Paris containing antibiotics for a prevention of experimental osteomyelitis, using 45 rats, which were divided into 3 groups. In the Group 1, a defect was made at the proximal metaphysis of the tibia, inoculated by Staphylococcus aureus sensitive to Cephradine and Tobramycin and then filled with plaster of Paris pellet. In the Group 2, a defect was filled with Cephradine loaded plaster of Paris pellet. In the Group 3, a defect was filled with Tobramycin loaded plaster of Paris pellet. Then we observed the healing process of the bone defect in the point of view of the gross findings, radiologic findings and histologic findings at 4th, 8th and 12th week after operation. The results of this study were as follows:l. In the control Group;all 30 cases were infected. 2. In the Group 2;only 4 of 30 cases were infected. 3. In the Group 3;all 30 cases were not infected. 4. The plaster of Paris filled into the defect was absorbed continuously and stimulated the new bone formation.