A new approach to the fluorescent labelling of glycoproteins was developed utilizing the aldehyde-reactive N-amino anthranilic acid (NA₃) moiety linked to a dansyl fluorophore. The presented synthetic method is based on the conjugation of isatin as a “masked” anthranilic acid, thus eliminating the need for the use of protecting groups. Fluorescence properties and chemical stability of the prepared molecules were evaluated, resulting in the selection of a conjugate directly connecting the dansyl moiety and aldehyde-reactive NA₃ through a sulfonamide linkage for further studies. NaIO₄-mediated oxidation of the glycosylated protein fetuin followed by rapid fluorescent tagging and native gel electrophoresis afforded glycoprotein detection. The detection limit of the described method was 18 ng of protein, providing sensitivity sufficient for the detection of abundant glycosylated serum proteins.