The chemical structures of P1 A was identified by complete acid hydrolysis, partial acid hydrolysis, periodate oxidation-Smith degradation, methylation analysis, IR and NMR. The results showed that P1 A had a backbone consisting rhamnose, mannose, glucose and galactose. The side chain possessed arabinose and xylose. 1-->, 1-->6 and non-reducing terminal linkages existed in polysaccharide P1A, but there are doubling amount of 1-->2 and 1-->4 linkages. Oxidable linkage of P1 A accounted for 45%, and inoxidable linkage of P1A accounted for 55%. Mannose, glucose and galactose were mainly linked by 1-->2 linkage. Rhamnose, arabinose and xylose were mainly linked by 1-->2 and 1-->4 linkages. PlA contained beta-Glc(1,6)-,beta-Gal(1,3)-,beta-Man(1,4)-beta-Rha,-Glc(1,4)-, Glc(1)-,-Gal(1,4)- and Man(1)-.