Abstract: In order to study the immunomodulative effect of ginkgo biloba polysaccharide(GBP)on mouse lymphocytes,lymphocyte suspension was prepared by sterile isolation of mouse spleen lymphocytes. Blank group,positive group(levamisole with final concentration of 5 μg/mL)and ginkgo biloba polysaccharide treatment group(final concentration of 25,50,100,200,400 μg/mL)were set up for the experiment. The effects of the GBP on the lymphocyte proliferation were detected by MTT assay,the cell cycle were detected by flow cytometry,the secretion of cytokines IL-4 and TNF-γ were detected by ELISA,and the mRNA relative expression levels of IL-4 and TNF-γ were detected by qRT-PCR. The results showed that the proliferation index of lymphocytes in GBP treatment group and the positive group was significantly higher than that in the blank group(P<0.01).Compared with the positive group,lymphocyte proliferation index in the 200 μg/mL GBP treatment group was lower than that in the positive group,but there was no statistical significance(P>0.05). Compared with the blank group,the proportion of G₀/G₁ in the 25~400 μg/mL GBP group decreased significantly,while the proportion of S and G₂/M cells increased significantly(P<0.01). The proportion of G₀/G₁ in 200 μg/mL GBP group was lower than that in the positive group,while the proportion of S and G₂/M cells was higher than that in the positive group,with statistical significance(P<0.01). Compared with the blank group,the IFN-γ/IL-4 ratio of the 25、100 and 200 μg/mL GBP treatment group was significantly lower than that of the blank group(P<0.01),and the IFN-γ/IL-4 ratio of the 400 μg/mL GBP treatment group was significantly higher than that of the blank group(P<0.01).Compared with the positive group,the IFN-γ/IL-4 ratio of the 100 and 200 μg/mL GBP treatment group was lower than the positive group,but there was no statistical significance(P>0.05). Compared with the blank group,the secretion of cytokines IFN-γ、IL-4 and its mRNA expression in the GBP treatment group and the positive group were significantly higher than those in the blank group(P<0.01).Compared with the positive group,the secretion of cytokines IFN-γ、IL-4 and its mRNA expression in the 200 μg/mL GBP treatment group were lower than those in the positive group,but there was no statistical significance(P>0.05). Therefore,ginkgo biloba polysaccharides can improve the immune function of mice by increasing the proliferation of spleen lymphocytes,reducing G₀/G₁ cell block,promoting DNA synthesis,promoting the secretion of cytokines IFN-γ、IL-4 and its mRNA expression,and maintaining the dynamic balance of IFN-γ/IL-4(Th1/Th2).