The Momordica charantia (MC) fruit has been documented to possess antidiabetic properties. However, these studies were not without controversy surrounding the blood glucose-lowering ability and the mechanism of action in diabetes therapy. In an effort to evaluate such claims in the Jamaican MC species known as cerasee, aqueous extracts of the unripe fruit were studied in normal and diabetic rats. Normal male Sprague-Dawley rats were divided into groups (n = 6) orally administered distilled water, 10% dimethyl sulfoxide (DMSO) solution, the aqueous extract (400 mg/kg body weight) and glibenclamide (15 mg/kg body weight), respectively prior to assessment of fasting blood glucose (FBG) concentration. The oral glucose tolerance test (OGTT) was conducted in normoglycaemic rats orally administered distilled water, 10% DMSO solution, glibenclamide (15 mg/kg body weight) or aqueous extracts of the fruit (200 and 400 mg/kg body weight). Blood glucose concentration was also monitored in streptozotocin-induced diabetic rats administered the aqueous extract (250 mg/kg body weight) or water vehicle after an overnight fast. The aqueous extracts showed no hypoglycaemic or antidiabetic activity. However, the administration of the aqueous extracts (200 and 400 mg/kg body weight) resulted in significant improvement in glucose tolerance of glucose-primed normoglycaemic rats during the OGTT. These data suggest that the glucose-lowering mechanism of the Jamaican MC fruit species likely involves altered glucose absorption across the gastrointestinal tract.