The raccoon dog (Nyctereutes procyonoides viverrinus) has recently become common in urban environments in Japan. We predicted that, like other carnivores adapted to urban environments, raccoon dogs in urban areas should have smaller home ranges than those in rural areas. We investigated the size of home ranges of raccoon dogs in the Akasaka Imperial Grounds, a 51-ha green area in central Tokyo. Between August 2012 and August 2014, 7 adult males and 4 adult females were radiotracked. Mean (± SD) home range size of these 11 raccoon dogs (100% minimum convex polygon = 17.6 ± 13.0 ha; 95% fixed kernel = 8.3 ± 5.7 ha) was smaller than that of raccoon dogs in rural areas obtained in previous studies, and core areas (75% local convex hull) averaged 3.7 ± 4.1 (SD) ha. We detected no seasonal changes in home range size. These results were consistent with the notion that urban carnivores typically have small home ranges. The small home range size seems to be explained by abundance of food resources, restricted environment, and the high population density of raccoon dogs in the urban green area.