Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used to determine the structures of anhydroicaritin glycosides by the MS/MS experiments of anhydroicaritin glycosides and their methylated derivatives. With high accuracy FT-ICR-MS provides much information about the structures of compounds, FT-ICR-MS shows the great potential application in the structural characterization of unknown compounds. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used to determine the structures of anhydroaritin glycosides by the MS / MS experiments of anhydroaritin glycosides and their methylated derivatives. With high accuracy FT-ICR-MS provides much information about the structures of compounds, FT-ICR-MS shows the great potential application in the structural characterization of unknown compounds.