Abstract: Atechnique of fast atom bombardment ionization in conjunction with colli-sional activation(FAB-MS/MS)has been successfully applied to structural analysis of saponins.FABmass spectra exhibited protonated or sodium adduct molecular ions,which may be used for unambiguous assingment of the molecular weights of the glycosides.The collisional activation spectra of the selected quasi-molecular ions(M+H)⁺gave a series of characteristic fragment ions promising to give a clear picture for defining the sequences of the constituent saccharide units of the glycosides and for identifying the glycone.The experimental results show that the MIKESspectra can also provide sequence information just as CAspectra do but the sensitivity of the former is much less than that of the latter.Compounds 1 and 2 are known compounds.The structural analysis results of these compounds by this technique are in agreement with that reported in the literature by conventional methods.Compounds 3 and 4 are two new compounds.