In Sado island, many habitat restoration programs are being carried out to establish the wild population of the Japanese crested ibis. However, these restoration activities have a potential downside that provide suitable habitat for invasive species like bullfrog. When habitat restoration for crested ibis is planned, ecological characteristics and distribution of bullfrog should be considered. To clarify the prey items and habitat selection of bullfrog in Sado island, we analyzed stomach contents of bullfrog and factors affecting their density. From the stomach contents of 189 adult bullfrogs, 82 animal species were identified as prey items, and particularly crayfish was main prey. Body size and ovary mass of bullfrog in ponds with crayfish were larger than that in ponds without crayfish.　The density of bullfrog was correlated with density of prey animals such as crayfish, aquatic insect, fish, and so on, rather than physical environment such as vegetation cover, water depth, terrestrial vegetation height, and so on. Our study suggested that the density and distribution of bullfrog in Sado island was determined by prey resources, particularly, crayfishes.