The paper is focused on the problem of the Unknown Self (which is understudied in personality psychology). The author turns to the “Confessions” by Aurelius Augus­tinus as a source of psychological knowledge about the Unknown Self and explains new opportunities of this text for the study of personality. A personological methodology used in the research of the Unknown Self assumes the unity of references to the text of culture and its hermeneutic analysis, to theoretical psychological knowledge about the personality and to the individual experience of knowing the Self that has a universal value. A conceptual model of the hermeneutics of the Unknown Self in the text of “Confessions” has been developed and applied. This model was used to provide the explication, analysis and synthesis of Augustinus’s self-statements related to the Unknown Self. The developed reflexive-hermeneutic model of the Unknown Self of Aurelius Augustinus is presented in the paper. The main areas of study (philosophical, cultural and psychological) of the “Confessions” in modern scientific contexts were considered in order to substantiate scientific novelty of the study. The study resulted in new hermeneutic data that indicate the significance of the theme of the Unknown Self in the text of “Confessions”; Augustinus’s comprehension of not knowing the Self in various areas of external and internal life and in relation to oneself, to others and to a highly significant Other; the psychologically subtle phenomenology of Augustinus’s experiencing the Unknown Self; various hypostases and structural constituents of the Self that for Augustinus represent objects and “tricks” of not-knowing; the individual and cultural value of knowing the Self that is fulfilled in a continuous reflective dialogue with God as the Other; Augustinus’s profound and intimate appeal to God as Thou as a condition for discovering the unawareness of the Self; Augustinus’s attitude to the Thou that is assumed to be a source of overcoming this unawareness of the Self and renewal of the self-relation of the Self; the attainment of revelations about the Self in questioning, prayer and repentance before the Thou; and such richness and extent of self-relation, and such “self-completion” in knowing the Self, in which the Self can “fill up” and “merge” with the higher Other.