Abstract: To investigate the characteristics of mass spectra of some drug metabolites, solutions of glucuronide conjugates of N-(4-ethoxyphenyl)-2-hydroxyl-benzamide (etofesalamide), 4-(3H-1,2-dihydro-1-pyrrolizinone-2-methylamino)-benzoic acid, 5-hydroxypropafenone and propafenone were analyzed using electrospray ion trap mass spectrometry in a multi-stage full scan mode performed on a Finnigan LCQ instrument. Sample solutions were directly introduced into the ESI source at a flow rate of 15～30 μl·min^-1 by a syringe pump. The mass spectrometer was operated in the negative ion mode. A full scan mass spectra of each analyte provided quasimolecular ion m/z M-1, and full scan MS² and MS³ spectra gave characteristic fragment ions m/z 175 and m/z 113, respectively, which were derived from the glucuronate moiety of each analyte. The proposed interpretation of m/z 175 is the negative ion of glucuronic acid with a loss of 18 u (H₂O), which produces m/z 113 after further losing 18 u (H₂O) and 44 u (CO₂). Fragmentation pathway has been established for each analyte. The results show that quasimolecular ion m/z M-1 and the characteristic fragment ions m/z 175 and m/z 113 in the multi-stage full scan mass analysis of each analyte can be predicted for future structure elucidation or quantitative determination of glucuronide conjugates by LC/MS.