This paper aims to analyze the mysticism in Walt Whitman’s Leaves of Grass and to compare with the theories of mystics scholars such as William James, Friedrich Schleiermacher, Richard Bucke, and Paul Tillich. Mysticism is a transcendent consciousness to experience the ecstasy and transcendence, which destroys the self or expands the ego. The mystical aspect of Whitman’s spirituality was expressed in his poetry as being one with the God/the Universe who was alive in his inner soul that Whitman called his soul. “Song of Myself” was found to be a dramatic representation of his mystical experiences. This paper analyzes “Song of Myself” and other poems in Leaves of Grass and identifies each step involved with mystical experiences. The first stage is to enter into a mystical state and meet his own soul. The second stage is to be awakened to his own self. The third stage is to purify his self. The fourth stage is a union with the Absolute. The fifth stage is to emerge from the mystical state. “Song of Myself” shows mystic experience processes exactly as a bible of mysticism.