A new alkaloid, nuphamine,1,2) C15H23O2N isolated from the roots of Nuphar japo-nicum DC. has been given the formula (I), in which the remaining unsettled problem was the configuration about the side chain double bond. The present paper deals with the absolute configuration of nuphamine. The action of thionyl chloride on nuphamine (I) gave a chloro compound (II),2) which, when kept standing in dilute hydrochloric acid, re-formed I. Attempts to direct toward the ring closure of II to III were unsuccessful recovering only the starting material, but when heated with potassium hydroxide in methanol solution, I afforded O-methylnuphamine (IV) C16H25O2N (picrolonate: m.p. 178°). These facts suggested that I would be represented by the formula (VIII). Furthermore, the configuration was studied by the measurement of nuclear magnetic resonance spectra of I, IV and (')-anhydronupharamine∗4'3) (VI) derived from (')-nupharamine (VIII). © 1965, The Pharmaceutical Society of Japan. All rights reserved.