Objective: To evaluate the anti-hyperglycaemic and hypoglyaemic effect of ethanol root extract of Sphenocentrum jollyanum (SJ) Pierre (Menispermaceae) in alloxan diabetic rabbits. Materials and methods: Alloxan diabetic rabbits (n = 5) were administered graded doses (50, 100 and 200 mg.kg–1) of the extract or glibenclamide (10 mg.kg–1) or vehicle (distilled water) for 15 days. Blood was collected i.v. from auricular vein on days 0, 3, 5, 7, 9, 11, 13, 15 for glucose estimation by oxidase method. In the oral glucose tolerance test (OGTT), rabbits received the extract (1 g.kg–1) or glibenclamide (0.01 mg.kg–1) or vehicle and 30 minutes later received oral glucose load (1 g.kg–1). Glucose was estimated at 30 minutes, 1, 2, 3 and 4 hours. The hypoglycaemic activity was assessed on normoglycaemic rabbit that received extract at 100, 250 and 500 mg.kg–1 and estimated at 0, 4, 8 and 12 hours. Results: The extract significantly (p < 0.05) enhanced glucose reduction by decreasing the peak glycaemic level and the area under curve in OGTT compared to the untreated. In alloxan diabetic rabbit, the extract produced significant dose dependent decrease in glycaemia from day 3 of oral treatment with comparatively higher activity than glibenclamide treatment. It also exhibited marked hypoglycaemic effect at 500 mg.kg–1 with lowest glycaemic reduction of 54.5 ± 7.7 (30.1%). The pancreatic histology showed focal areas of beta cells necrosis with significant number of the cells normal, suggesting that the extract may have effectively attenuated the diabetogenic agent inflammatory response. Conclusion: The ethanol root extract of SJ was very effective in lowering blood glucose.