Microbial transformation of 20(S)-protopanaxatriol (1) by Mucor spinosus afforded two new and eight known metabolites. The structures of the metabolites were identified as 12-oxo-20(S)-protopanaxatriol (2), 23,24-en-25-methoxyl-20(S)-protopanaxatriol (3), 29-hydroxyl-20(S)-protopanaxatriol (4), 20(S),24(S)-epoxy-dammaran-3 beta,6 alpha,12 beta,25-triol (5), 12-oxo-27-hydroxyl-20(S)-protopanaxatriol (6), 12-oxo-26-hydroxyl-20(S)-protopanaxatriol (7), 12-oxo-23 beta-hydroxyl-20(S)-protopanaxatriol (8), 12-oxo-11 beta-hydroxyl-20(S)-protopanaxatriol (9), 12-oxo-15 alpha-hydroxyl-20(S)-protopanaxatriol (10), and 12-oxo-25,26-en-15 alpha-hydroxyl-20(S)-protopanaxatriol (11). Among them, 3 and 11 are new compounds. The metabolites 3, 10 and 11 showed the more potent inhibitory effects against seven cell lines than the substrate.