Sugar consumption has been increased in recent days according to an improvement in living conditions. It is generally accepted that sugar is one of the causes of caries and that diabetes mellitus is closely related to the periodontal diseases. This investigation was designed to gain informations on the influence of overdosage of sugar and/or high blood sugar level on the periodontal tissue. 12 rats weighing about 1.5Kg were divided into 4 groups, control one and 3-day, 7-day, 14-day ones after daily administration of 30-50 gm of sucrose. The results were as follows: 1. Daily adminisration of 30-50 gm of sucrose elevated blood glucose level as much as 10-20 mg% than before. 2. Epithelial keratinization was gradually conspicuous to the dosage of sucrose. 3. The severity of inflammatory infiltration was also increased to the dosage of sucrose. 4. Inflammatory infiltration was encountered in marginal gingiva more than other periodontal tissue.