Because of the decreasing number of individuals and the unsuccessful reproduction of captive gorillas, the documentation of the development of gorilla infants is attracting much attention in Japan. The aim of this study was to document the social development of a captive gorilla infant in Higashiyama Zoo. We recorded the activity budgets, proximity data, approach, and moving away of this infant, Ai, at 7 and 19 months of age, and the ways of infant-carrying at 19 months of age. In her first year, Ai started to be independent of her mother and to approach a nonkin female gorilla by herself. During the same period, the two ways of infant-carrying which gorilla infants display in different developmental stages were shown: carrying in the ventro-ventral position and ventro-dorsal position. These results revealed the developmental change of the relationship between Ai and each adult individual. The accumulation of case reports such as this study will help to understand the development of gorilla infants in captivity. Based on such understanding, the welfare and management of the captive gorilla population in Japan may be improved.