This paper investigates Mary Oliver’s Twelve Moons, focusing on the gradual changes occurring in her ecopoetics expressed through the poetry collection. In her earlier poems, Oliver refrains from crossing boundaries between humans and nature, and shows respect toward diverse elements constituting nature. Then, in the poems contained in Twelve Moons, Oliver’s poetic speaker starts to pursue intimate connection with nature, glancing at a possibility of going “into the body of another,” which characterizes her later poetry. The deployment of personification in “The Black Snake” signifies the beginning of Oliver’s direct contact with nature and her desire to imitate the perfectness of natural beings. In “Bone Poem,” she further develops an anti-dualistic view of nature, in which all the creatures exist in inter-connected relations and ultimately get unified in the process of cyclic circulation. Finally, Oliver attempts an imagined “transformation” into natural things in “Aunt Leaf” albeit temporarily, bordering on the experience of going “into the body of another.” These poems testify Oliver’s scrupulous pursuits to approach and interact with nature, which still provide valuable lessons in the contemporary world suffering tremendously from human beings’ ill-constructed relationships with nature.