b-lapachone (1) has entered phases I and II clinical trials for the treatment of solid tumors and the therapeutic efficacy of b-lapachone is closely related to its metabolic process. In order to contribute to a better understanding of human metabolism of b-lapachone, Cunninghamella elegans ATCC 10028b was used as a microbial model of mammalian metabolism to biotransform b-lapachone and two new glycosylated derivatives were produced. The chemical structures were elucidated as 6-hydroxy-2,2 dimethyl-3,4-dihydro-2H-naphtho[1,2-b]pyran-5-O-b-D-glucopyranoside (2) and 5-hydroxy-2,2-dimethyl-3,4-dihydro-2H-naphtho[1,2-b]pyran-6-O-b-D-glucopyranoside (3) by 1 H NMR, 13C NMR, HMBC, HMQC, COSY and HRMS analyses. The major derivative (3) displayed a lower activity against breast cancer cell line SKBR-3 (IC50 = 312.5 mM) than b-lapachone (IC50 = 5.6 mM), but did not show cytotoxicity against normal fibroblasts cell line GM07492-A, whereas b-lapachone was highly toxic (IC50 = 7.25 mM). These metabolites were reported here for the first time and are similar to those that occur in phase II of human metabolism