The role of sialyloligosaccharides of secreted glycoproteins is still unclear because of the difficulty in the preparation of sialylglycoproteins as homogeneous substrates. We selected erythropoietin (EPO) as a target molecule and examined the chemical synthesis of EPO glycoforms varying glycosylation position and the number of human type biantennary sialyloligosaccharides. EPO-polypeptide (166 amino acids) was designed to divide into 6 segments including glycopeptides and these were synthesized by solid phase peptide synthesis under the Boc conditions. Segment coupling of these 6 segments by native chemical ligation yielded homogeneous EPO glycopeptides. We also examined folding protocol to obtain correctly folded EPO glycoforms. According this procedure, we synthesized the several EPO isoforms varying the oligosaccharide number and glycosylation positions. In vivo assay with mice for erythropoiesis, synthetic EPO glycoforms showed suitable biological activity. In this presentation, we discuss how glycosylation pattern change the biological activity of erythropoietin.