In the course of studies on the metabolism of saikosaponins, which are the main constituents of Bupleurum falcatum L., five new compounds derived from saikosaponins a, c and d were isolated after incubation with acid and snail enzyme. On incubation of saikosaponins a and c at 60°C in a 1 N sulfuric acid-dioxane solution, saikosaponins g and i possessing a homoannular diene moiety at C-9 (11), 12 were isolated, and their structures were elucidated as 3β, 16β, 23, 28-tetrahydroxyoleana-9 (11), 12-diene 3-O-β-D-glucopyranosyl-(1→3)-β-D-fucopyranoside and 3β, 16β, 28-trihydroxyoleana-9 (11), 12-diene 3-O-β-D-glucopyranosyl-(1→6)-[α-L-rhamnopyranosyl-(1→4)]-β-D-glucopyranoside, respectively. Furthermore, on incubation of saikosaponins b₁, g and b₂ with snail enzyme for 12h at 37°C, prosaikogenins A, H, and D were formed ; they were identified as the 3-β-D-fucopyranosides of saikogenins A, H and D.