There are many clinical and experimental evidences indicating the involvement of oxidative stress in pathogenesis of diabetes mellitus and its complications. Increased oxidative stress is due to excessive reactive oxygen species generation due to persistent hyperglycemia and a sharp reduction of antioxidants defenses and the tissue antioxidant status. An imbalance between oxidative stress and antioxidative defense mechanisms in diabetics can result in cell and tissue damage and accelerate diabetic complications. There is mounting evidence that a general increase in antioxidant status achieved by dietary supplementation can help to diminish oxidative stress in diabetics and profoundly contribute to reduce the severity of the disease. Plant antioxidants by virtue of their antioxidant activity, may exert beneficial implications for diabetes management. This book highlights the various methods to assess antioxidant activity of medicinal plants. It also contributes to ascertain the utility of plant antioxidants to markedly complement the anti- diabetic therapies by reducing the oxidative stress in diabetics and its associated complications.