Argon laser (5w) was irradiated on the femoral bone of Wister rats. These rats were sacrificed on 1, 2, 3, 7, 14, 21 and 28 days from the beginning. Repair process of carbonized bone tissue was studied from the view points of histological observations.Carbonization zone, Degeneration zone and Normal zone could be differentiated by H.E staining. On 1st day,no hematoma (fibrinclot) could be seen at the irradiated site. Fragmentation and absorption of carbonization and degeneration zone began on 7th day following invasion of fibroblasts. After 3 weeks, separation of carbonization and degeneration zone could be observed, but cartilago didn't appear yet. Appearance of cartilago and new bone trabecula was found at 4th week.From this study, the repair process of carbonized bone delayed comparing to usual fracture healing. It is considered that defect of primary hematoma at the irradiated site and carbonization are concerned with delayed bone repair.