This article discusses the activities of the Sino-Japanese Society of the Study of Esoteric Buddhism, which was active in North China from the early 1930s until the end of the Second World War. The organization was founded by Yoshii Hōjun, a young priest of the Japanese Shingon sect. It attracted the support of a wide range of actors, including a range of former Beiyang government politicians, Japanese diplomats, as well as prominent members of the Japanese community in North China. It had contacts in the Japanese military that have garnered the Society the reputation of having been a front for Japanese intelligence operations. This article critically investigates these claims and seeks to understand the relationship between religion and politics manifested in the Study Society for Esoteric Buddhism. Its history reflects the fraught relations between the two nations as well as between the various interest groups on both sides and thus provides a window into the complexities of pre-war North China in the 1930s.