The author has observed the tissue reaction of the absolute alcohol infection of rat oral mucosa. 0.5ml absolute alcohol was injected subcutaneously on the mucobuccal fold of rat. And the rats were sacrifieced at intervals of one day, 3rd, 1 week, 2 week and 4 week after alcohol injection. The microscopic tissue sections were made and stained with hematoxylin and eosin. The results were are as follows; 1. Degeneration and shrinkage of fibroblasts and coagulative necrosis were observed one day to and three day after alcohol injection. 2. Although coagulative necrosis and tissue degeneration occurred, the inflammatory infiltration was not prominent especially there were scarcely any polymorphonuclear leukocytes in that field. 3. Granulation tissue with moderate small round cell infiltration were replaced the necrotic area at one week after injection and the fibroblast proliferate into the granulation tissue at two week group. 4. At four week after injection, the damaged area recovered by fibroblastic proliferation and collage formation, but there were