The instant invention provides a method for the differential diagnosis of inflammatory bowel disease which comprises,determining the relative ratio of G0 oligosaccharide represented by formula (I):to G2 oligosaccharide represented by formula (II):wherein G represents galactose, M represents mannose, GN represents N-acetylglucosamine and F represents fucose in serum IgG oligosaccharide fraction obtained from a patient with inflammatory bowel disease or a patient with suspicion of inflammatory bowel disease, anddiscriminating inflammatory bowel disease based on the obtained ratio.
