Diabetes mellitus (DM) is a major public health problem with increasing worldwide incidence. The main causes for increase in incidence of DM are inactivity, obesity and changes of dietary habits. Investigators think that the changes in the awake-sleep cycle may also contribute to higher incidence of DM in recent years. Melatonin is an important component of the circadian system. Numerous experimental studies have demonstrated that melatonin has many beneficial actions.Melatonin is a potent antioxidant, reduces inflammatory process, lowers blood pressure, improve lipid profiles. Collectively, these data suggest that melatonin may be useful in control of blood sugar in patients with DM.