Four new hasubanan alkaloids, stephamiersine (1), epistephamiersine (2), oxosteph-amiersine (3) and stephasunoline (4) were isolated together with seven known and three unidentified alkaloids from Stephania japonica Miers (Menispermaceae). Among these new alkaloids, 1 and 2 were found to be epimeric isomers with respect to the C-7 methoxyl group. - Permanganate oxidation of 1 gave 3, and borohydride reduction of 1 and 2 gave the highly stereoselective products, dihydrostephamiersine (6) and dihydroepistephamiersine (5). On mild treatment of 5 with hydrochloric acid gave 4. Acetolyses of 1, 2, 5 and 6 gave the phenanthrene derivatives, 7, 8 and 9, respectively. Further, both 1 and 2 were converted to the conjugated carbonyl compound (14) which was obtained from dihydro-16-oxohasubanonine (17a) (17b). On the other hand, the stereochemistry of 1, 2, 3 and 4 was elucidated by nuclear magnetic resonance (NMR) spectroscopic studies as follows: the C-7 methoxyl group of 1 has the a-axial and that of 2 and 4 has the β-equatorial configuration, and the hydroxyl group of 4 has the β-axial one. On the basis of the above chemical correlation coupled with the spectral arguments, the constitution of the new alkaloids was represented as drawn in the formulas, 1, 2, 3 and 4. © 1975, The Pharmaceutical Society of Japan. All rights reserved.