Abstract: A peptide-polysaccharide, ABAB showing immunological activity was isolated from Achyeanthes bidentata B1. It was shown to be homogeneous by HPLC and optical rotatlon analysis. Its molecular weight Was estimated to be2.3×10⁴. It composed of D-glucuronic acid, D-galactose, D-galacturonic acid, L-arabinose and L-rhamnose in molar ratio of 12:2: 3: 1: 1. Reduction of carboxyl groups, methylation analysis, periodate oxidation, Smith degradation and IR analysis showed that ABAB possesses a main chain composed of (1→4 )-D-glucuronic acid and (1→4)-D-galacturonic acid residues. The non-reducing terminal residues in the side chains were L-arabinose and L-rhamnoe. ABAB contained 24.1% of peptides composed of glycine. giutamic acid, asparticacid and serine.