From the aerial parts of Smilax sieboldi MIQ. a new steroidal sapogenin, laxogenin (I), was isolated together with tigogenin and neotigogenin. The analytical values of I corresponded to formula C27H42O4 for sapogenin and C29H44O5 for the acetate. On Huang-Minlon reduction I afforded tigogenin (II), and on sodium borohydride reduction of I, β-chlorogenin (III) and chlorogenin (IV) were obtained in ratio about 85 : 15. The chromic acid oxidation of I afforded a diketone (V), m.p. 229∼231°, which was proved to be identical with 25D-allospirostane-3, 6-dione. From these results the structure of laxogenin was assumed to be 3β-hydroxy-25D, 5α-spirostan-6-one and this assumption was confirmed by the synthesis of this compound from 5, 6-epoxydiosgenin (XI).