Abstract: Objective To study the best composition and dose ratio of polysaccha ride-combination in vivo,and to explore the mechanism of its immunoenhancement.Methods This expremental was designed based on the L27(3¹³)o rthogonal.Four polysaccha rides were selected as experimental factors and they were set to three doses from scratch.After polysac charides combination in traperitoneal in jection to the mice,the immune organ index,the spleen nature killer cell activity were studied.Results The best composition of polysaccha ride-combinations on the immune activity was the composition of lichenan(8 mg/kg),ganode ran(16 m g/kg),astraga lan(8 m g/kg)and lentinan(16 mg/kg).In the high,middle,low dosage levels,the index of spleen were 1.214±0.153,1.327±0.168,1.052±0.074,respectively.The index were all higher than the control group(0.554±0.069)significantly(P<0.05 or P<0.01).The index of thymus were 0.261±0.065,0.273±0.049,0.241±0.053,and were all higher than that of the control group(0.140±0.025)significantly(P<0.05 or P<0.01).Conclusion The ploysaccharide-combination with most apropriate doses ratio maybe provide the most effective way for pooducing the strongest immune-enhancing agent.