Diabetes mellitus (DM) is the commonest endocrine disorder that affects more than 100 million people worldwide (6% population). It is caused by deficiency or ineffective production of insulin by pancreas which results in increase or decrease in concentrations of glucose in the blood. It is found to damage many of body systems particularly blood vessels, eyes, kidney, heart and nerves. In this book aimed at finding hypoglycemic activity of selected plants such as Tinosporacordifolia, Costuspictus (Insulin plant), Ocimum tenuiflorum, Andrographis paniculata, Pongamia pinnata. Most of the drugs used in the Siddha or Ayurvedic system are said to be free from side effects. Hence, if a drug is developed for hyperglycemic problems from this system, it would be a better alternative for treatment after conducting clinical studies.