Disaccharides and linear oligosaccharides were labeled with p-aminobenzoic ethyl ester (ABEE) chromophore and analyzed by negative ion electrospray ionization mass spectrometry (ESIMS). The formation of glycosylamines rather than reductive amination in the labeling reaction produced many characteristic fragment ions under in source collision-induced dissociation (CID). These ions provided unambiguous assignment of the position of the glycosidic linkages. This approach was extended to the analysis of linkages and the sequence of the linkages of several linear oligosaccharides. Additionally, the anomeric configuration of ABEE-labeled 1-3-, 1-4- and 1-6-linked glucose disaccharides could be differentiated according to the relative abundance of characteristic ions. Disaccharides with the same linkage but different monosaccharide compositions could be analyzed by on-line coupling of high-performance liquid chromatography with ESIMS.