Abstract: The fragmentation mechanism of Liranaftate studied by fourier transform-ion cyclotron resonance mass spectrometry or fourier transform-ion cyclotron resonance tandem mass spectrometry is described. The relatively fragmentation mechanism and pathways are discussed in details. And a rearrangement principle is found by a hepta-atom-ring intermediate. These hypothetical results are confirmed through exact mass measurements, which shows the error between the exact masses and theoretical masses only less than 2 μD, and these mechanisms are further conformed by tandem mass spectrometric experiments. The difference between the mass spectra acquired by MALDI and EI are investigated, and the results are proved that the rearrangements are achieved by a hepta-atom-ring intermediate on the N atom belonged to pyridine ring of Liranaftate.