In present study, we investigated the antidiabetic effect of Momordica charantia(as well known “bitter melon”). This study was conducted to determine antidiabetic mechanism of Bitter Melon Extract (BME). We measured blood glucose, insulin, glucagon level in a Sprague-Dawley rat model of high-fat diet/streptozotocin(HFD/STZ)-induced diabetes. Five experimental groups were used: normal, HFD/STZ, BME 62.5 mg/kg HFD/STZ, BME 125 mg/kg HFD/STZ and BME 250 mg/kg HFD/STZ. BME was orally administered to the rats every other day for 9 weeks. Results showed that fasting blood glucose levels were significantly lower in the BME 125 mg/kg(150.17 ± 20.22 mg/dL) and 250 mg/kg(124.17 ± 22.17 mg/dL) groups than in the vehicle group(188.83 ± 26.63 mg/dL)(p<0.05). In addition, glucagon levels were lower in the three BME treatment groups than in the vehicle group(p<0.05). Oral glucose tolerance tests revealed that the BME 250 mg/kg group had significantly(p<0.05) reduced 120-minute blood glucose levels and areas under the curve. Our results suggest that BME induces antidiabetic effects via the reduction of glucagon and blood glucose levels.