The microbial transformation of a steroidal alkaloid, dictyophlebine (1) with Rhizopus stolonifer (ATCC 10404) afforded three oxidized metabolites 2-4. Compound 2 was found to be a new product. These metabolites were structurally characterized on the basis of modern spectroscopic techniques. Their inhibitory activity towards acetyl- and butyrylcholinesterase has been evaluated and the new product 2 has been found to be more potent than the parent compound and other metabolites.