The toplications of 50% nicotin paste in oral mucous membrane of male mice weigh-ingabout 30 gram, were executed for 10, 15 and 20 days. And the tissues were observed in HE and PAS stain. The findings observed are as follows; I. Hyperplastic changes were revealed in underlying connective tissue and spinous cell layer. There were moderate vasodilatations with out edema but PAS reactions were dictinctive. in 10th day of experiment. II. There was remarkable increment of mortality up to 40percent and weight loss, but microscopic findings were not significant differences on than 10th days, in 15th day of experiment. III. Cellular anisocytosis, hyperchromatism and degenerations were observed in spinous cell layer, and vascular engergement in connec tivetissues were observed. And the mortality was up to 70 percent in 20th day of experment.