The inhibitory effects of various synthetic oligosaccharides (1-8) on anti-lipid IV antiserum binding activity were examined by ELISA (enzyme linked immunosorbent assay). Compound 8, containing an epitope GlcA-4Me beta 1-4Fuc of lipid IV, inhibited but precursors (1-5) of lipid IV did not inhibit the binding activity. In addition to the nonreducing end disaccharide derivative (6) having a methyl group at position 4 of glucuronic acid, its analogous compound (7) having no methyl groups was synthesized and their inhibition activities were compared. Moreover, the inhibitory effects of compounds (1-5) were examined using each antiserum.