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A rapid and stable method consisting of high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry was established for the identification and differentiation of common diastereoisomeric ursane-type triterpenoids at the C-3 position. Two characteristic fragment ions, [M–H–H2O–CO2] and [M–H–H2O–HCOOH], exhibited significant stereochemical effects and were utilized to distinguish 3-OH epimers. Based on reference standards, the abundance of the fragment ion [M–H–H2O–HCOOH] in 3β-OH compounds in the MS3 experiment was dramatically higher compared to [M–H–H2O–CO2]; however, for 3α-OH compounds, the product ion [M–H–H2O–CO2] was noted to be higher than [M–H–H2O–HCOOH]. Energy-resolved mass spectrometric experiments were carried out to support the differentiation of these diastereoisomeric triterpenoids at the C-3 position. Using this method, a total of nine ursane-type triterpenoids from a plant crude extract, including four pairs of epimers at the C-3 position, were identified and distinguished rapidly. Furthermore, offline Fourier transform ion cyclotron resonance tandem mass spectrometry was also performed to assign accurate elemental compositions. Copyright © 2011 John Wiley & Sons, Ltd.