Background: Diabetes mellitus is a heterogeneous group of disorders characterized by abnormalities of carbohydrate, protein and lipid metabolism. Type 1 diabetes mellitus is an autoimmune disease caused by destruction of pancreatic beta cells and characterized by defect in insulin secretion while type 2 diabetes mellitus results from abnormalities in insulin secretion and/or insulin action or both. Objectives: The present study was conducted to investigate the clinical hypoglycemic effects of Allium cepa in type 1 and type 2 diabetic patients. Results: In assessment of hypoglycaemic activity of Allium cepa in type 1 and type 2 diabetic patients, ingestion of crude Allium cepa (100 g) caused a considerable reduction in fasting blood glucose levels by about 89 mg/dl in relation to insulin (145 mg/dl) in type 1 diabetic patients and it reduced fasting blood glucose levels by 40 mg/dl, compared to glibenclamide (81 mg/dl) in type 2 diabetic patients, 4 hours later. The same dose of crude Allium cepa produced a significant reduction in the induced hyperglycemia (GTT) by about 120 mg/dl compared to water (77 mg/dl) and insulin (153 mg/dl) in type 1 diabetic patients and considerably reduced GTT by 159 mg/dl in relation to water (55 mg/dl) and glibenclamide (114 mg/dl) in type 2 diabetic patients, after 4 hours. Conclusion: It was evident that, crude Allium cepa produced hypoglycemic effects, thus it could be used as a dietary supplement in management of type 1 and/or type 2 diabetes mellitus.