Abstract: OBJECTIVE To study the preventing and treating effect of Sinopodophyllum Hexundrum on breast cancer tumors in mice model and its mechanism. METHODS The BALB/c mice were injected with 4T1 cells combined with immune suppressor. According to weight， all mice were randomly divided into 6 groups， normal group， model group， Tamoxifen group (4.1 mg/kg) and high， medium and low Sinopodophyllum Hexundrum dose group（1.2， 0.6， 0.3 g/kg）， and administrated drugs intragastrically. After 25 days， quality of tumors and changes of visceral index， WBC count and histomorphology were detected. RESULTS Sinopodophyllum Hexundrum significantly reduced tumor weight and decreased tumor， spleen and thymus index， and WBC count. Tissue section showed promotion of tumor cell differentiation. CONCLUSION Tibetan medicine Sinopodophyllum hexandrum has significant preventing and treating effect on breast cancer， and the mechanism may be related to immunosuppression.