Abstract: The purpose of this study was to investigate the effect of ursolic acid(UA)on anti-tumor and intestinal bacteria in H22 tumor-bearing mice. In this experiment,the models of tumor-bearing mice were established by injection of colonic cancer cells H22. Then,the mice were randomly divided into normal group,model group,positive control group(cytoxan group)and the groups treated with low,middle and high dose of UA,respectively. After 3 weeks,the tumor inhibition rate,index of liver and spleen were calculated. The concentrations of T-cell subsets,interleukin-2(IL-2)and tumor necrosis factorα(TNF-α)in serum were detected. The effect of ursolic acid on intestinal bacterial community structure and diversity in H22 tumor-bearing mice were analyzed using high-throughput sequencing platform. The results showed that UA could significantly reduce the xenograft tumor weight compared with the model group(P<0.05). The level of T-cell subsets,IL-2 and TNF-α in mice treated with middle and high dose of UA significantly increased by comparing with the model group(P<0.05). Compared with normal group,PCA analysis indicated that there were significantly differences in intestinal bacteria of model group and group treated with low dose of UA. However,there were no significant difference in intestinal bacteria of groups treated with middle and high dose of UA by comparing with normal group(P>0.05). At phylum and family level,the proportion and distribution of intestinal bacteria in mice treated with UA were closer to the normal group than model group. Compared with model group,the relative abundance of Akkermansia and Lactobacillus significantly increased in mice treated with UA(P<0.05),and the relative abundance of Muribaculum significantly decreased(P<0.05). It indicated that UA could inhibit the growth of tumor and increase immunity of mice,accelerate the recovery of intestinal bacteria imbalance associated with tumor.