A rapid and sensitive method for the identification and quantification of armillarisin succinate ester (ASE), which is a patent drug, is described. The method used liquid chromatography-ion trap mass spectrometry (LC-IT-MS/MS). The ASE standard solution was directly infused into IT-MS for collecting MS(n) spectra. The major fragment ions of ASE were confirmed by MS(n) at m/z 333, 233, 202, 189 and 163 in negative ion mode, and m/z 335, 217, 189,175 and 161 in positive mode, respectively. The possible main fragment ions cleavage pathways were studied between in positive-ion mode and in negative-ion mode. Quantification was performed using the transitions m/z 333 --> 233 in negative mode. The method is reliable and reproducible, and the detection limit is 2 ng/mL. The method was validated in the concentration range of 1.0 - 50 microg/mL, intra- and inter-day precision ranged from 1.98% to 4.06%, and the accuracy was 97.5-106.2%. The mean recovery of ASE was 97.2-105.3% with RSD less than 4.35%. A LC-IT-MS/MS has successfully applied to determine the ASE in its medicinal preparations.