The negative secondary ion mass spectrometry,in combination with the stereoselectivederivatizations with substituted boronic acid RB(OH)_2,was used in the analysis of fourteen oligosac-charides.The mass spectra of the derivatives provide information on their linkage Positions and iso-merism of the individual monoscaccharide units.The results indicated that among the derivativesof the oligosaccharides analyzed,those with 1—4 and 1—6 linkages all presented the ion peaks at m/z287,sometimes one more peak at m/z 449.Furthermore,a relationship was found between the linkagepositions and the intensity orders of the derivative ions.Finally,the derivatives of the disaccharideswith a galactose presented an intense ion peak at m/z 347,and those of oligosaccharides with 1—6linkage to a galactose at terminal presented the ion at m/z 317.In the case of oligosaccharides witha fructose residue,characteristic ion of m/z 155 was produced.The conditions of stereoselectivederivatizations and mass spectrometry were studied,in order to obtain a better reproducibility of themass spectra.