In this paper, we investigated the dynamics of aging of the estrous function of female rats kept in the conditions of standard vivarium lighting and receiving luzindol - the blocker of melatonin receptors. Every three months, daily, for two weeks, vaginal smears were taken from the animals and cytological examination of the vaginal contents was conducted. Despite different mechanisms of the development of melatonin system failure (a decreased production of melatonin and a blockade of melatonin receptors), the effects of the influence on the ovulatory function are similar. In case of the blockade of melatonin receptors, the appearance of premature signs of aging of the reproductive function in rats was observed. It was manifested by an increased duration of ovulatory cycle; a decrease in the number of regular cycles; the emergence of irregular cycles; a decrease in the number of short estrous cycles and an increase of long cycles; the early development of persistent estrus.