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Biosynthesis of glycoproteins in the endoplasmic reticulum employs a quality control (QC) system, which discriminates and excludes misfolded malfunctional glycoproteins from correctly folded one. In the QC system, UDP-glucose:glycoprotein glucosyltransferase (UGGT) recognizes misfolded glycoprotein bearing high-mannose type N-glycan and glucosylate it so that the misfolded proteins can interact with molecular chaperones calnexin/calreticulin to attain correctly folded structure. As chemical tools to study glycoprotein quality control system at molecular level, we systematically synthesized misfolded homogeneous glycoproteins bearing high-mannose type oligosaccharide. Interleukin 8 (IL-8) is a nonglycosylated protein consisted of 72 amino acid residues and two disulfide bonds between Cys7–Cys34 and Cys9–Cys50. As a model, we incorporated high-mannose type (Man9GlcNAc2) oligosaccharide at the Asn36. The full-length glycosylpolypeptide chain was successfully synthesized by native chemical ligation between N-terminal 33-amino acid peptide-thioester and C-terminal 39-amino acid glycopeptide, which was prepared with Fmoc-Asn derivative having high-mannose oligosaccharide on the side chain.Extensive folding experiments of chemically synthesized homogeneous IL-8 glycopeptide yielded correctly folded glycoprotein with native disulfide bond patterns as well as misfolded glycoproteins with non-native disulfide bond patterns and a disulfide bond-linked misfolded homodimer. Other misfolded glycoprotein models with one and no disulfide bond and glycopeptides consisted of C-terminal 39-amino acid residues were also prepared. Transfer of glucose residue to these homogeneous glycoprotein analogues by UGGT was analyzed by using LC-MS. This assay proved that the critical endoplasmic reticulum folding sensor enzyme, UGGT recognizes misfolded glycosyl-IL-8s with different preferences. The most favored substrate was a homodimer which exhibits molten globule-like hydrophobic nature, and the least favored substrate was a correctly folded glycosyl-IL-8. Glycoproteins and glycopeptides having non-native disulfide bonds were also favored substrates.