The antioxidative property and inhibitory effect of otogiri-sou (Hypericum erectum) leaf tea on postprandial blood glucose elevation were investigated. The otogiri-sou leaf contains a large quantity of such polyphenols as chlorogenic acid, caffeic acid, and epicatechin. Tea extracts with boiled water containing 2, 5, and 10% of otogiri-sou leaves showed strong DPPH radical scavenging activity. The lowering effect of otogiri-sou leaf tea on α-glucosidase activity was enhanced by the hot tea extracts containing at least 2% otogiri-sou leaves. The postprandial blood glucose level in human subjects after ingesting boiled rice was measured subsequent to an oral administration of otogiri-sou leaf tea. The subjects were assigned to two groups, each with a mean postprandial blood glucose level of 139 mg/dl. Otogiri-sou leaf tea significantly suppressed the increase of blood glucose level in those subjects whose postprandial blood glucose level was higher than the mean. These results suggest that the intake of otogiri-sou leaf tea prevented an increased postprandial blood glucose level by inhibiting the digestive absorption of sugars. These results suggest that the intake of otogiri-sou leaf tea prevented an increased postprandial blood glucose level by inhibiting the digestive absorption of sugars.