This paper considers the interrelation and coexistence between human and nonhuman in nature in William Blake’s (1757-1827) Songs of Innocence and Songs of Experience (1789-1794). The paper looks at his poems in the light of ecocentrism, especially the theories of Lawrence Buell (1939- ) and Ashton Nichols (1953- ), who articulate ecocentrism as a word which expresses the interconnection between human and nonhuman in nature and environment. The word, ecocentrism, denotes nature and environment as the central and essential parts of the world to represent them as a web or system wherein all members and parts, including human and nonhuman, are related and connected to each other so closely that they cannot exist and live separately and lonely. By human, it refers to who is a creature in the web, who links to other creatures and entities so closely that he cannot be isolated from them. The linkage and coexistence are the matter which can be viewed in some of the poems of William Blake’s Songs of Innocence and Songs of Experience. Blake watches environment and nature carefully, and in some of the poems of two mentioned collections such as “The Echoing Green,” “Nurse’s Song,” “Holy Thursday,” “The School Boy,” to name just a few, he illustrates a situation of life in which human has close relation and connection to other creatures. According to Blake, human and nonhuman have such a vital relationship so that no one can live without the others. All creatures and beings in an organism have an effect on each other, and they are interrelated. The paper shows interconnection and coexistence between human and nonhuman in Blake’s Songs of Innocence and Songs of Experience due to portrayal and representation of nonhuman creatures in the world. It defines some nonhuman terms such as nature and environment and then focuses on the interrelation and coexistence between human and nonhuman in Blake’s Songs of Innocence and Songs of Experience in accordance with ecocentrism.