Abstract: AIM　To investigate the chemical structure and activities of CPB54, a polysaccharide purified from Cynanchum paniculatum (Bunge) Kitagawa whose molecular weight was estimated to be 6.0×10⁵ by HPLC. METHODS　Sugar composition analysis, methylation analysis, partial hydrolysis and Carbon-13 NMR were used to determine the chemical structure and activities of CPB54. RESULTS　Sugar analysis indicated that it composed of arabinose, rhamnose and galactose in molar ratios of 0.8∶0.5∶1.0. Methylation analysis, partial hydrolysis and NMR data showed that the main chain of the polysaccharide composed of 1,4 linked galactose residues and 1,2 linked rhamnose residues. Arabinosyl residues as side chain mainly located at the O-4 of rhamnosyl residues. Pharmacological results showed this polysaccharide had stronger effect on promotion of spleen and lymphocyte proliferation. CONCLUSION　CPB54 is a new polysaccharide with stronger effect on promotion of spleen and lymphocyte proliferation.