Many naturally occurring proteins are glycoproteins. The glycan moieties of glycoproteins play an important role in numerous biological events such as cellular interaction. Since the structures of the glycan moieties change in physiological and unphysiological conditions, such glycans are often used as biomarkers of various diseases, particularly cancers. “Lectin Blotting” is a simple and easy method to estimate overall structures of the glycans with use of a variety of lectins that bind specifically to monosaccharides or glycan units on glycoproteins separated by SDS-polyacrylamide gel electrophoresis followed by blotting to membranes. By employing this method, we found a marked change in the N-acetylgalactosaminylation of glycoproteins between cancerous and non-cancerous parts of human breast tumors.