Background: Melatonin is a hormone secreted by the pineal gland in the brain. It helps regulate other hormones and maintains the body’s daily rhythm, telling us when to fall asleep and when to wake up. Ever since we developed electricity and the lightbulb, we have been decreasing our body’s secretions of melatonin by being exposed to bright light after it is dark. Jet lag, shift work and poor vision also affect regular melatonin levels. In Chinese Medicine, melatonin could be likened to the functions of healthy Liver energy. Melatonin also helps control the timing and release of female reproductive hormones. It helps determine when a woman starts to menstruate, the frequency and duration of menstrual cycles, and when a woman stops menstruating (menopause).Materials and Methods: This is review article.Results: Melatonin intake also improved pregnancy rates, which were 19.6 percent among women taking supplements compared with 10.2% for the women not taking any. Melatonin has strong antioxidant effects.Preliminary evidence suggests that it may help strengthen the immune system. This could have an important effect on male fertility. In anin vitro study involving semen samples taken from 52 men receiving counseling for infertility, semen samples were incubated for 30 minutes with or without 1mm melatonin. Positive correlations were found between melatonin concentrations and sperm concentration, motility and morphology. Additionally, samples incubated with melatonin showed improved percentage of motile and progressively motile cells, and decreased static cells.Conclusion: High endogenous melatonin concentrations enhance sperm quality and short-term in vitro exposure to melatonin improves aspects of sperm motility.