Abstract: OBJECTIVE To observe the protective effect of Swertia mileensis T. M. Host W. L. Shih on chronic liver injury in mice and its regulation on spleen T lymphocyte subsets in mice. METHODS A model of chemical liver injury in mice was induced by intraperitoneal injection of carbon tetrachloride(CCl₄). Serum aspartate aminotransferase(AST), alanine aminotransferase(ALT), total protein(TP) and total bilirubin(TBI) were detected in mice. HE staining was used to observe liver tissue morphology; flow cytometry was used to detect changes in the number of CD3⁺, CD4⁺ and CD8⁺ positive cells; the proportion of CD4⁺/CD8⁺ ratio were calculated, and they were compare with the model group and the control group. RESULTS S. mileensis had protective effects on chronic liver injury induced by CCl₄ in mice, which could significantly decrease serum ALT and AST levels(P<0.01) and increase TP content compared with model group(P<0.01). Compared with model group, the low dose group of S. mileensis had a down-regulating effect on CD3⁺ cells(P<0.05), and there was a significant difference in the up-regulating effect on CD8⁺ cells and the down-regulating effect on the ratio of CD4⁺/CD8⁺(P<0.01); the high dose group of S. mileensis had a statistically significant effect on the up-regulation of CD8⁺ cells and the down-regulation of CD4⁺/CD8⁺ ratio(P<0.05). CONCLUSION S. mileensis has protective effect on CCl₄-induced chronic liver injury in mice, and its mechanism may be through the regulation of T lymphocyte subsets, affecting immune function.