Exercise and diet control are essential for the management of diabetes mellitus. Beneficial effects of exercise have been established. Exercises improve the control of glucose level, decrease cardiac risk factors and prevent type 2 diabetes mellitus. Exercise can cause hypoglycemia or hyperglycemia, cardiac attack, dehydration, foot problems and aggravation of diabetic complications. Pre-exercise medical evaluation is needed to prevent the unwanted effect of exercise. Diabetic patients who have ketonuria and high blood glucose level(more than 250mg/dL) should postpone exercise until the problems are solved. Diabetic patients should enjoy their activities and do warming up and cool down exercise. Vigorous aerobic exercise, 60~85% of maximal oxygen uptake, 20~60 minutes at a time, 3~5 times a week is recommended. Moderate aerobic exercise, 40~60% of maximal oxygen uptake, more than 30 minutes at a time, over 5 times a week is also recommended instead. Muscle strengthening exercises, 2~3 times a week should be added. To prevent hypoglycemia during exercise, the dose of insulin should be reduced. If the patient suffer from hypoglycemic symptom, he or she should take glucose immediately. Therefore diabetic patients should carry some simple carbohydrates. To prevent dehydration during exercise, proper hydration and clothes must be prepared. Wearing well fitting shoes, frequent check up for any wounds on foot are needed to prevent diabetic foot complications. Diabetic patients have the rights to have good quality of life. Regular proper exercise could improve their quality of life.