This article examines the role of the doctrine of angels in Augustine’s theological system and demonstrates its fundamental significance in his controversy with Manichaeism. Unlike the Manichaean worldview, which was based on the eternal dualism of Light and Darkness and regarded evil as an independent reality, Augustine sought to provide an integrated response to the problem of evil through his interpretation of the creation and destiny of angels. Within this framework, the creation of angels signifies the original goodness of creation, their fall exemplifies the operation of free will, and their fidelity constitutes the foundation of the City of God. Taken together, these three dimensions reveal that evil is not an eternal substance but rather the privation of good arising from the free choice of creatures. Thus, for Augustine, the doctrine of angels was not merely a cosmological issue but a strategic instrument for rejecting the two Manichaean principles and defending the unity of the Creator and the goodness of creation. The methodology of this study is based on historical–theological analysis, with information gathered through a library-based approach to Augustine’s primary works and contemporary scholarship. By focusing on the interrelation of creation, fall, and fidelity of the angels, this study highlights their unique contribution to Augustine’s explanation of evil and to the formation of his anti-Manichaean theology.