In the modern Japanese poetry, there are many works that grasp the creature appearing in poetry as main theme, not a simple poetic material. Especially Hagiwara- sakutaro, a representative poet of the Taisho Period, is actively expressing a feeling of vitality through many plants, animals, and microbes. While this actively extends the range of the biological world having remained in the world of mortals, This fundamentally denies a fixed idea that only human beings are superior to other creatures . Hagiwara makes full use of a special sense near to illnese or perversion in expressing these contents. So a diseased or deformed animal often appears in his animal poetry. In this study, I analyzed these poetic features of his through Poetical Works of "Tsukinihoeru" and "Aoneko". After all, The consideration for various expressions of the creature appearing in the poetry of Sakutaro will be an important text in synthetically grasping the organic mutual relation between living things constituting the biological world.