This study attempts to identify the reasons why Yukai, a scholar-monk of the Shingon School in the Muromachi era, presumed that the Zo-mondo was not Kukai's work, despite the fact that it had generally been believed to be his work until the early Kamakura era. Yukai's conclusion has been accepted in academia. Therefore, in order to confirm the foundation of Yukai's supposition, this study examined quotations of the Zo-mondo in Yukai's works. The findings are that the Zo-mondo contradicts Kukai's Sokushin jobutsu-gi and that the Xindiguan jing, which had not yet entered Japan in Kukai's times, is excerpted in the Zo-mondo.
