A new hasubanan ester-ketal alkaloid, named stephabenine, was isolated from the fresh fruits of Stephania japnica Miers (Menispermaceae). Alkaline hydrolysis of the new base gave benzoic acid and a basic component, whose proton nuclear magnetic resonance spectrum was identical with that of authentic N.O-dimethylsteohine. © 1983, The Pharmaceutical Society of Japan. All rights reserved.