Abstract: The MS characteristic of eight common paralytic shellfish poisoning (PSP) toxins (GTX1, GTX4, GTX2, GTX3, dcGTX2, dcGTX3, C1 and C2) were investigated by electrospray ionization multi-stage mass spectrometry (ESI-MSⁿ) in negative ion mode. The results show that the quasi-molecular ion peak M-H^- (base peak) of each PSP toxin is detected by ESI-MS. Stability characteristic fragment ions are observed by the neutral loss of -H₂O and -NHCO for ESI-MS² detection， and the MS² spectra of PSP toxin isomers are different, which can provide experimental basis for qualitative and quantitative determination of sulfur containing PSP toxins by ESI-MS². ESI-MS³ detection is performed for the main characteristic fragment ions of the target toxins produced during ESI-MS² analysis. The main MS³ characteristics of the fragment routes are also discussed. This study can help to offer the reference and basis for determination of sulfur containing PSP toxins by electrospray ionization mass spectrometry in negative ion mode.