OBJECTIVE： To investigate the effect of total saponins of Man medicine Thladiantha dubia root （TSTR） on the expressions of CD3+， CD4+and CD8+ in spleen tissue of rats with type Ⅱ collagen-induced arthritis （CIA）， and explore its mechanism in the treatment of rheumatoid arthritis （RA）. METHODS： 8 rats were taken as normal control group （NC group）， the others 72 rats were injected mixture of bovine type Ⅱ collagen and Freund’s complete adjuvant in tail and back to induce CIA model. The 50 modeled rats were randomly divided into model group （MC group）， tripterygium polyglycoside （TG） group （12 mg/kg， positive control）， TSTR low-dose， medium-dose， high-dose groups （20， 40， 80 mg/kg）， 10 in each group. Rats in medicine groups were intragastrically administrated for 35 d， once a day； rats in NC group and MC group were intragastrically administrated equal volume of distilled water. Ankle swelling degree of rats was determined， arthritis indexes were calculated， HE staining was used to observe the lesions in synovial tissue， and immunohistochemistry was used to detect the expressions of CD3+， CD4+， CD8+ in spleen tissue of rats. RESULTS： After 35 d of administration， ankle swelling degree， arthritis indexes， CD4+ expression in spleen tissue， and CD4+/CD8+ ratio in MC group were significantly higher than NC group （P＜0.05 or P＜0.01）， expressions of CD3+， CD8+ were significantly lower than NC group （P＜0.05）； and there was congestion and massive inflammatory cell infiltration in synovial tissue. The ankle swelling degree， arthritis indexes， expression of CD4+ in spleen tissue， and CD4+/CD8+ ratio in administration groups were significantly lower than MC group （P＜0.05）； the expressions of CD3+， CD8+ in spleen tissue in administration groups were significantly higher than MC group （P＜0.05）； TG group， TSTR medium-dose and high-dose groups showed mild congestion and a small amount of inflammatory cell infiltration in synovial tissue of rats， and TSTR low-dose group showed no obvious congestion or inflammatory cell infiltration. CONCLUSIONS： Up-regulating the expressions of CD3+， CD8+ and down-regulating the expression of CD4+ may be one of the mechanisms of TSTR in the treatment of RA； and with best efficacy when the TSTR dose of 20 mg/kg.