The liquid secondary ionization mass spectrometry of oligosaccharide anions is investigated with an external source quadrupole Fourier transform mass spectrometer (FTMS). Selected linear and cyclic oligosaccharides are analyzed to determine the performance of the external source FTMS in the anion mode. Fragmentation behavior of disaccharides is characterized and related to the fragmentation behavior of larger oligomers. General correlation is found between the linkages and the fragment ions observed.