We investigated the effects of hot spring water drinking in Kawayu on blood glucose levels and insulin secretions. Kawayu hot spring water is characterized “acid alum vitriol hydrogensulfide” with a pH of 1.98. First, a glucose tolerance test (GTT) was performed on eight non-diabetic people and nine diabetic patients after drinking of tap water or Kawayu hot spring water at a one-week interval. Plasma glucose levels after pre-drinking spring water showed significantly (p=0.05) decreasing compared with those after pre-drinking tap water. Serum immunoreactive insulin (IRI) levels after predrinking hot spring water were tend to be higher at the early phase of GTT than those after pre-drinking tap water. And, we confirmed the correlation between the total decreasing of blood glucose levels and the reactions of insulin secretion at early phase of GTT after spring water drinking. Second, GTT was performed on seven diabetic patients before and after four-week drinking of Kawayu hot spring water. The results showed that hemoglobin A1c levels and total cholesterol levels ware decreased significantly (p<0.05). Total blood glucose levels of tested GTT were, however, almost similar before and after drinking treatment. These findings suggest that drinking of Kawayu hot spring water is beneficial for diabetic patients.