To search for the endogenous glyco-epitope in Caenorhabditis elegans, we synthesized labeled Galβ1-3Fuc and Galβ1-4Fuc and examined their binding affinity for C. elegans galectin LEC-6 using frontal affinity chromatography analysis. We developed a new strategy for synthesizing the labeled saccharides, in which the labeling unit, the 2-aminopyridine moiety, is coupled with a spacer unit derived from D-mannitol. Our results indicate that Galβ1-4Fuc is the endogenous glyco-epitope present in C. elegans N-glycans.