Abstract: Loganin was investigated systematically by electrospray ionization tandem mass spectrometry (ESI-MSⁿ) to propose the logical fragmentation pathways. Product ion mass spectra examined at high mass resolution allowed unambiguous determination of the elemental composition of fragment ions by sustained off-resonance irradiation/collisioninduced dissociation (SORI-CID) method in fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Through hydrogen and deuterium exchange, the fragment path of Loganin is further confirmed. Experiment demonstrates that M+Li⁺ and M+Na⁺ ions can provide complementary useful structural information for structure analysis of Loganin.