Structural elucidation was carried out on protofarrerol (I), a component of Leptorumohra miqueliana H. ITO (=Polystichopsis miqueliana TAGAWA) (Aspidiaceae). Examinations were made on the infrared, ultraviolet, and nuclear magnetic resonance spectra of I and its derivatives and, from the decomposition reaction of I, it was found to be 5, 7-dihydroxy-6, 8-dimethyl-2-(1'-hydroxy-4'-oxo-2'-cyclohexenyl)-4-chromanone. One of the decomposition products of I, 5, 7-dihydroxy-6, 8-dimethyl-2-(4'-oxocyclohexyl)-4-chromone (XII), was synthesized. I is the first natural flavanoid compound in which the B ring is not a benzene ring and, since I easily forms a flavanone by dehydration, it is of interest from biosynthetic viewpoint.