Preeclampsia is a complex pathological process which development signifi cantly depends on a decrease in melatonin levels of pregnant women as a result of the pineal gland and placenta dysfunction. The most important hormone of the pineal gland is melatonin, which is a derivative of tryptophan – an essential amino acid. Melatonin is a powerful natural antioxidant. When it’s levels are decreased, there is a risk of preeclampsia progression as a pathological condition of pregnant women, accompanied by high blood pressure, systemic multiple- organ failure and even cerebral edema and convulsions.Thus, although preeclampsia is considered a disease of the mother, it should rather be considered as a pathological condition of the placenta that aff ects both mother’s and fetus health. As the key factor of placental diorders is an oxidative stress, many researchers consider melatonin to be a potentially useful option for treating preeclampsia. It is noted that pregnant women with preeclampsia have a decrease in nocturnal concentrations of melatonin in comparison with healthy pregnant women that may indicate about pineal gland dysfunction in preeclampsia. Therefore, the normalization of melatonin levels may be a promising direction in the treatment of pregnant women with preeclampsia.