We can find the Mariological texts of St Thomas Aquinas in only a few of his works. Nonetheless, in his teaching he focused on Mariological issues of importance to theology. This article aimed to present Aquinas’ theology on the question of the fullness of grace in the Blessed Virgin Mary. In the first part of this article, in addition to the general historical context, the basic content on Aquinas’ theology of grace is introduced. In the following chapters, the author of the article, based on the teaching of St Thomas, sought to present the effects produced by the presence of full grace in the life of Mary, followed by a discussion of its three forms, which St Thomas related to the stages of the life of the Mother of Jesus. In summary, firmly grounded in Christoligy, St Thomas’ Mariology links the truth of Mary’s ‘full grace’ to the literal presence of Christ in her womb. Consequently, Aquinas regards the Incarnation of Christ as the sole source of the graces received by the Mother of Jesus.