Stephaoxocanine (1), a dihydroisoquinoline alkaloid bearing an oxocane ring, was isolated from the tubers of Stephania cepharantha cultivated in Japan, together with five known alkaloids. The structure was established on the basis of the spectroscopic data of 1 and its dihydro derivative (2), and the absolute configuration was determined by the modified Mosher's method. By comparison of the CD spectral data with that of 2, the revised absolute stereochemistry of excentricine (3) was proposed as 3a.