This paper aims to study Yeats and Nietzsche through Nietzsche’s “Will to Power” in some of Yeats’s poems. In 1902, Yeats first read Nietzsche’s works; through Nietzsche Yeats’s voice turned into a manly voice. An internal conflict appears as a Mask theory in Yeats's poetry. Self and Anti-self (Mask) are two components in the Mask theory. While Will is an internal and subjective self, Mask is a social and objective self. The internal conflicts between Will and Mask determine the human mind. Yeats’s “Mask” and “Ego Dominus Tuus” exemplify Will to Power as an internal conflict. Nietzsche’s Will to Power is a concept of quantity based upon the law of energy preservation refusing causality, the movement ascending and descending and the eternal recurrence of the same. Similarly, Yeat in his A Vision has rewritten a European history based upon the theory of opposite forces in a gyre. He classifies personalities into 28 types based one phases of the moon. Assigned to Phase 12, the phase of heroic man who overcomes himself, Nietzsche is a forerunner; who is fragmentary, violent, and subjective. Perspectivism, a kind of Will to Power, is a plural and relative point of view that is classified into 4 categories; Will to Power as knowledge ("Leda and the Swan"), art ("Ego Dominus Tuus"), love ("Crazy Jane Grown Old Looks at the Dancers"), and truth ("Demon and Beast"). In conclusion, Yeats’s later poems achieve a creative and powerful voice when he thinks and speaks with Nietzsche; in particular, Nietzsche’s Will to Power, a philosophy of Being and Becoming, is echoed in some of Yeats’s later poems.