This graduation work describes the character and work of St. Augustine and his understanding of mercy, which is difficult to understand outside the context of his life, the time in which he lived and his own theological abstentions. The work explores the concept of mercy, as Augustine perceives it, then the opponents of Augustine and their perception of God's mercy are emphasized. The work contains the very core and roots of Augustine's thoughts, and the construction text is being supplemented in order to show his opinion of God's mercy as vividly as possiblele. The first chapter deals with Augustine's life, where his way of sin and grace is described. Thanks to his biography, we understand why he takes such a stance on mercy. He himself experienced God's mercy in his life and understood it correctly. The second chapter is the main part of the paper describing Augustine's perception of God's mercy. Augustine's definition of mercy is presented, and the term, which is closely tied, is briefly explained. It was shown that he learned about God's mercy and that the theme of God's mercy was marked by Augustine for the rest of his life. The third chapter deals with the importance of mercy for today and the Church in general, that is, the echo of Augustine's struggle for mercy today. Insight into this problem can be seen in many works, and the encyclic of Dives in Misericordia, Pope John Paul II and bull Misericordiae vultus, Pope Francis, are highlighted.