This study was undertaken to observe the histopathologic changes of the extraction wounds of diabetic rats when exposed to hyperbaric oxygen. A total of 50 rats (Spraque-Dawley strain) were used, which were all induced with diabetes using streptozotocin before the experiment. The experimental group was exposed to hyperbaric oxygen at 2.5atm. for 2 hours a day during the experimental period. The obtained results were summarized as follows : 1. Severe infiltration of inflammatory cells was observed in the initial stages of both the control and experimental groups. The infiltration showed a decreasing tendency at 3rd week in the experimental group, while severe inflammatory infiltration observed in the control group during the entire experimental period. 2. There was abundant proliferation of capillary blood vessels at 1st week after extraction in the experimental group, while moderate capillary growth in the control group was observed at 1st week after extraction. 3. Osteoblastic activity was started at 1st week after extraction in the experimental group, but there showed markedly delayed appearance in the control group, which showed at 2nd week after extraction. 4. The proliferation of fibroblasts showed rather in the experimental group at 1st week, but it was moderate in the control group at 1st week, 2nd week and 3rd week. 5. Epithelialization of the extraction wound was started at 2 days after extraction and reached its peak at 3rd week in the experimental group, while control group seemed to be delayed and incompleted during the experiment. With regard to these results, hyperbaric oxygen therapy disclosed an effective results on the healing of the extraction wound in diabetic rats under exposure at 2.5 atm for 2 hours daily.