When analyzing the Mariology of St. Gregory of Nyssa, one theme stands out: the reality of the hypostatic union and as a direct consequence the divine motherhood. So the more frecuent statements about Mary are those contained in Adversus Apollinarem. The reader can see for himself that, years before Nestor, the question which this gave rise to was even then clearly formulated, extensively dealt with and clearly resolved. Continuing on from this point, St. Gregory comments on the Blessed Virgin in a throrough and loving manner. He quietly defends the Marian privileges with firm conviction, and above all, her virginity, placing in relief her role in the salvation of men. St. Gregory in short finds himself immersed in the environment of his contemporary theologians, and he knows how to incorporate into his theological thinking as well as in his spiritual life all of those mariological questions which come down to him through the secular Christian tradition. Our study is divided into two parts. In the first, we consider four sections which are especially long and significant: the Sermo de Annuntiatione, the Sermo in diem natalem Domini, the De Tridui Spatio and the homilies ln Canticum Canticorum. In the second part, we go on to study the most important Marian themes, from a systematic point of view: the divine maternity, her perpetual virginity, the role of Mary in the economy of Salvation. There are three fundamental texts of Sacred Scripture which St. Gregory cites to speak of Mary. These texts are always understood in the identical sense: Lk 1, 26 ss.; Is 7, 17, and Prov 9, 1. All of these are cited for the purpose of discussing the virginal motherhood. St. Gregory's understanding of Is 7, 14 is always consistent and serene, because he found himself in close contact with the way in which the prior tradition had understood this text. The term parthenos is understood not as maiden, but as virgin in the strictest sense of the word. The prophecy not only announces that a maiden will conceive a child, but announces a great mystery: that a maiden will conceive as a virgin and that her virginity will remain intact in giving birth. Prov 1, 9 refers to the virginal motherhood: it is Wisdom itself which builds its own house; God, without the intervention of man, forms in the womb of Mary the body of the Lord. The terms theotokos is employed by St. Gregory in its fullest sense, especially directed at Apolinar and his theory that Christ was less than fully human. St. Gregory stresses that the union of the Word with his human nature took place at the very instant of conception, and points out that the title of theotokos is incompatible with the term anthropotokos. St. Gregory considers the virgin motherhood as a reflection or the eternal and incorruptible generation of the Word. Finally, St. Gregory fully developes the parallelism between Eve and Mary, and lovingly describes the Virgin at the foot of the cross, intimately united to her Son in the act of Redemption. He also calls Mary lmmaculate Virgin. The term evidently does not posses the defined limits which it would have in later theology. But what can be said is that with this term, with all of its underlying theology, the Saint from Nyssa is saying exactly that which is confirmed in the Doctrine of the Faith concerning the Inmaculate Conception of Mary.