Diabetes is a growing health concern worldwide and now emerging as an epidemic world over. Diabetes mellitus is a metabolic disorder characterized by chronic hyperglycemia or increased blood glucose levels, resulting from insufficient or inefficient insulin secretion, with alterations in carbohydrate, protein and lipid metabolism. Type-2 diabetes is the most prevalent form, of the total diabetics about 90% have type-2 diabetes, which is characterized by post-prandial hyperglycaemia (increase in blood sugar level after a meal). Many medicinal plants are reported to have insulin-mimetic effect, modulation of insulin secretion and inhibition of carbohydrate digesting enzymes. The currently available anti diabetic agents include sulfonylureas, thiazolidinediones and alpha glucos idase inhibitors and are widely used to control the hyperglycemia. These drugs fail significantly to alter the course of diabetic complications. They have limited use because of undesirable pathological conditions and high rates of secondary failure. This it is essential to look for more effective antidiabetic agents with fewer side effects. Traditional medicinal plants having anti diabetic properties can be a useful source for the development of safer and effective oral hypoglycaemic agents. More than 350 traditional plants are used in the treatment of diabetes mellitus, which have been recorded. Only a small number of these have received scientific and medical evaluation to assess their efficacy. However, plant remedies are the mainstream of treatment in underdeveloped regions. This review focuses on diabetes mellitus and the role of plants in the treatment of diabetes mellitus.