Yasuhiro Kajihara is a professor in the Department of Biological Sciences, Osaka University, with a particular interest in oligosaccharides and glycoproteins. In order to synthesize homogeneous glycoproteins, we have developed new efficient semi-synthetic methods. Short glycopeptide-thioesters are synthesized by solid phase peptide synthesis and non-glycosylated long peptides are produced by E. coli recombinant expression methods. Subsequently selective chemical activation is used for installation of C-terminal thioester and N-terminal cysteine surrogates. In this presentation, I would like to discuss efficient glycoprotein syntheses and the function of oligosaccharides of glycoproteins.