A new 1,3-diazetidin, named cinnatenuifolin, was isolated from the MeOH extract of the stems of Cinnamomum tenuifolium (Lauraceae). The structure of cinnatenuifolin was characterized by spectroscopic means as 2-((4-(4-hydroxy-3-methoxyphenyl)-1,3-diazetidin-2-yl)methyl)-3,5-dimethoxyphenol.