Oligosaccharides in glycoproteins have important roles for the expression of various biological functions.Co-existence of closely related oligosaccharides in glycoproteins (i.e., microheterogeneity) makes oligosaccharide analysis still a very challenging task despite the rapid advancements of mass spectrometry.To monitor the glycosylation profiles and the interaction of oligosaccharides with lectins, we evaluated the partial filling technique using lectins and exoglycosidases in capillary electrophoresis (CE).In partial filling CE, a lectin or exoglycosidase solution and a mixture of glycoprotein-derived oligosaccharides labeled with 8-aminopyrene-l,3,6-trisulfonic acid were introduced to a neutrally coated capillary in this order, and separated by application of a negative voltage.In lectin affinity CE, interaction of a lectin with each oligosaccharide in the mixture was observed as the specific retardation or dissipation of peaks, in addition to the size/charge separation of oligosaccharides by zone electrophoresis in the remainder of the capillary.The strength of the interaction with lectin was controlled by introducing an appropriate volume of lection solution.