The structures of raphanusanins A and B, growth inhibitors involved in phototropism of radish hypocotyls, were determined by X-ray crystallographic structure analysis and by spectral studies to be (3R*,6R*)- and (3R*,6S*)-3-[methoxy(methylthio)methyl]-2-pyrrolidinethione, respectively. Therefore, the previously proposed structure of these compounds of 2-piperidinethione skeleton should be revised.