This study was designed to investigate the hypoglycemic effects of Benincasa hispida (Wax gourd) in streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in the male rats by intravenous injection of STZ at a dose of 45 mg/kg dissolved in citrate buffer. The diabetic animals then had plasma glucose concentration of above 300mg/dl. The experimental groups were divided into five groups; normal, STZ-control and three Wax gourd groups (5%, 10% and 20% intake groups). Normal and STZ-control groups were fed on a AIN-93 diet and experimental groups were fed a AIN-93 diet with the Wax gourd powder (5%, 10% and 20%/kg diet) for 4 weeks. The body weight, diet intake and feed efficiency ratio (FER) were monitored. The blood glucose and cholesterol levels were determined everyweek. After 4 weeks, the rats were sacrificed and the levels of glucose, insulin, cholesterol, HDL-cholesterol, triglyceride and free fatty acids in plasma and levels of glycogen in liver and muscle were analyzed. Diabetic rats showed the lower weight gain compared to the normal rats. The weight gain and feed efficiency ratios in 15 and 20% Wax gourd groups were higher than in STZ-control group. The plasma glucose levels were significantly lower in all Wax gourd groups than in STZ-control group. The plasma insulin levels in diabetic groups were not significantly different compared to the normal group, but the level of 20% Wax gourd group was higher than other diabetic groups. The experimental diabetic groups showed the higher levels of muscle glycogen compared to STZ-control group. The lower levels of plasma cholesterol were noticed in 20% Wax gourd group throughout the experimental period. The plasma level of triglyceride was elevated in STZ-diabetic control and the levels were slightly decreased in Wax gourd groups. Rats of 10% Wax gourd group showed the lower levels of plasma free fatty acids. It is suggested, from the results, that the possibility of therapeutic or preventive use of wax gourd to the diabetes mellitus.