This study is an attempt to analyze Yeats’s early poetry in the light of his theory of the mask. For this purpose the writer of the present study has first proposed to define the ‘mask’ to investigate the theory and has reached the conclusion that the ‘mask’ is a Yeatsian term for an ideal image of life which is always opposite to the natural self or the natural world, and the theory of the mask has three aspects−aesthetic, moral, and philosophical−according to the role of the mask. The aesthetic meaning of the theory demonstrates Yeats’s argument on the nature, the source, and the touchstone of a work of art: art is the embodiment of the writer’s mask of life and his inner struggle between mask and life sets him to his creative work; the quality of a work depends upon the expression of this tragic war. And all the more important, Yeats’s strong belief in polarity of the two terms of conflict is clarified. The study of Yeats’s early poetry in terms of his theory of the mask has concluded that Yeats’s early mask is the very transcendent realm which Yeats’s early symbolism proposes to evoke and the main symbols used to express this ideal world are the images of Arcadian island across the sea, rose, the Irish mythic world and Maud Gonne; and the synthesis of Yeats's theory of the mask and symbolism in his early poetry causes some distortions in both his theory of the mask and symbolism. The nature of his transcendent world is conveyed not by the symbols but by the imperfect realities in spite of his strong belief that “divine essence” can only be evoked by the symbols; the nature of this ideal world has also been distorted: it is not the super reality lying beyond reality like Mallarme’s but only an ideal place where all the impurities and imperfections of the real world are removed or corrected. As for the theory of the mask, polarity, the most important basis of the theory, has been impaired: only the value and the love of the ideal world is emphasized, whereas those of the earthly life are restrained or its weaknesses and painfulness are stated to describe the ideal world.