This article deals with the religiosity of thanatology in Japan, which was introduced under the name shiseigaku (death and life studies) in the 1980s. Although many religious believers and scholars of religious studies have been connected with this field in Japan, religions are not necessarily highlighted by studies of Japanese thanatology. The Japanese pioneers of thanatology did not have clear ideas on the positioning of religion in this field, but they unconsciously merged their own faith into their discipline. Later, other scholars tried to re-construct this field by weakening its religious orientation. The Japanese case is in contrast to Taiwanese thanatology, in which the pioneers tried to position religious beliefs as the essential element of the field. Indeed, this difference was partially influenced by the religious traditions of both societies, but other factors such as the historical processes of this academic field and the private beliefs of researchers were important causes of that difference.