Abstract: AIMTo study the metabolites of guanfu base A hydrochloride (GFA) in rat urine. METHODS Rat urine was collected after iv injection of GFA. Phase I metabolites were identified by HPLC/MS and by comparison with authentic standards. Phase II conjugates were treated with either glucuronidase or sulfatase in presence or absence of glucuronidase specific inhibitor D-saccharic acid β-1,4-lactone. The aglycones were identified by HPLC/MS. RESULTS Phase I metabolites guanfu base I (GFI) and guanfu alcohol-amine (AA) were separated and identified in rat urine by comparison with authentic standards. Phase II conjugates, for which no authentic standards were available, GFA glucuronide and sulfate conjugates, GFI glucuronide and sulfate were separated and tentatively identified by hydrolysis with glucuronidase or sulfatase, the aglycones, GFA and GFI, were identified in rat urine. CONCLUSIONAfter iv injection of GFA, GFA is metabolized into GFI, AA, GFA glucuronide and sulfate conjugates, GFI glucuronide and sulfate conjugates in rat urine. The polarity of the metabolites is increased, and the effectiveness of them is lower than the parent drug.