The aqueous solution of dried powder of the Allium cepa was administered in doses of 100, 150 and 200 mg/kg body weight to normal and alloxan treated diabetic rabbits. The blood glucose levels were estimated before and 2, 4, 6 and 8 hours after the administration of the solution. The solution exerted a significant (p < 0.05) hypoglycaemic effect in both normal and diabetic rabbits. In normal rabbits, oral administration of 150 and 200 mg/kg doses caused decreased in blood glucose levels at 2,4,6 and 8 hours, while maximum decreased was at 6 hours. In the alloxan treated diabetic rabbits, 200 mg/kg dose only could produce significant decreased at 4,6 and 8 hours, while maximum decreased was at 6 hours. The doses used did not show acute toxicity or behavioural changes. It may be concluded that the plant contains one or more hypoglycaemic principles which can reduce the blood glucose in normal rabbits and in those with alloxan induced diabetes.