Endo-alpha-N-acetylgalactosaminidase catalyzes the release of Galbeta1-3GalNAc from the core 1-type O-glycan (Galbeta1-3GalNAcalpha1-Ser/Thr) of mucin glycoproteins and synthetic p-nitrophenyl (pNP) alpha-linked substrates. Here, we report the enzymatic syntheses of core 1 disaccharide-containing glycopeptides using the transglycosylation activity of endo-alpha-N-acetylgalactosaminidase (EngBF) from Bifidobacterium longum. The enzyme directly transferred Galbeta1-3GalNAc to serine or threonine residues of bioactive peptides such as PAMP-12, bradykinin, peptide-T and MUC1a when Galbeta1-3GalNAcalpha1-pNP was used as a donor substrate. The enzyme was also found to catalyze the reverse-hydrolysis reaction. EngBF synthesized the core 1 disaccharide-containing oligosaccharides when the enzyme was incubated with either glucose or lactose and Galbeta1-3GalNAc prepared from porcine gastric mucin using bifidobacterial cells expressing endo-alpha-N-acetylgalactosaminidase. Synthesized oligosaccharides are promising prebiotics for bifidobacteria.