A new hasubanalactam alkaloid, oxoepistephamiersine (1), was isolated together with known alkaloids, oxostephamiersine (2) and lanuginosine (3), from the petroleum ether extraction of the roots of Stephania japónica. The new alkaloid is the seventh hasubanalactam congener isolated from the Stephania genus. © 1984, American Chemical Society. All rights reserved.