This paper describes fragmentation modes of conventional and tandem mass spectrometry of the derivatives of monosialoganlioside GM1, including isopropyl monosialoganglioside GM1and acetyl lysomonosialoganglioside GM1. In the analysis of the former, it has been found that: (i) the abundant sodiated molecule of the lipid derivative is readily desorbed by positive-ion liquid secondary-ion mass spectrometry utilizing 3-nitrobenzyl alcohol as liquid matrix; (ii) the isopropyl derivatized-N-acetylneuraminic acid moiety can be detected by the positive-ion mode and collisionally induced dissociation tandem mass spectrometry; and (iii) the saccharide composition and sequence can be identified by negative-ion liquid secondary ion mass spectrometry. For the latter, the molecular mass, oligosaccharide sequence and modified ceramide moiety in the lipids can be characterized by coventional negative-ion liquid secondary-ion mass spectrometry and tandem mass spectrometry.