The antidiabetic effects of himeukogi leaf tea were investigated on KK-A^y mice, an animal model with type 2 diabetes. Five-week-old KK-A^y mice were administered the control with water or himeukogi leaf tea for 6 weeks (Experiment 1). Himeukogi leaf tea significantly inhibited the increases in fasting blood glucose and postprandial blood glucose after orally loading with glucose. In experiment 2, nine-week-old KK-A^y mice were administered the control with water or himeukogi leaf tea for 4 weeks. Himeukogi leaf tea significantly decreased the fasting blood glucose and postprandial blood glucose levels after orally loading with glucose. The blood glucose level of the himeukogi leaf tea group was significantly decreased in an insulin tolerance test. Moreover, the weight of white adipose tissue was also decreased in the himeukogi leaf tea group. These results indicate that himeukogi leaf tea may have beneficial effects on the management of type 2 diabetes mellitus.