Abstract: The fragmentation pathways of four triterpene glycosides from Apostichopus japonicus Selenka were investigated in negative ion mode by ESI-Q-TOF MS. The M-H^-ions were observed by ESI-MS, from which the molecular weights were obtained. The collision induced dissociation (CID) data of the M-H^-ions provide fragmentation pathways of the triterpene glycosides. Results show that four compounds have the same fragmentation pathway. The cleavage is initiated by a loss of 18 (20)-lactone residue from the aglycon, then consecutively loses monosaccharide residue of sugar chain, and finally yields a signature ion peak at m/z 423. These characteristic fragmentations will be helpful in identifying the structures of triterpene glycosides.