Disclosed is a synthetic AILIM extracellular domain which has high ligand-binding ability and a quality sufficient for a pharmaceutical product. Also disclosed is a method for synthesizing the synthetic AILIM extracellular domain. Specifically disclosed is a sugar chaim-added AILIM extracellular domain wherein a sugar chain is bound at a position corresponding to the 69-position of the amino acid sequence of human AILIM extracellular domain, said amino acid sequence being depicted in SEQ ID NO: 7, and no sugar chain is added at positions corresponding to the 3-position and the 90-position of the amino acid sequence.
