Abstract: Objective To study the function of CD4+CD25+Treg and effecter cells of mice with Lewis lung cancer were influenced by CTX and BCG therapeutic alliance, investigate the relationship of CD4+CD25+ Treg and the tumor, and provide experiment evidence for the tumor immunotherapy. MethodsThe models were established by injected CTX (25mg/kg) and after 7 days injected subcutaneously to the right axilla of C57BL/6 mice with subculturing Lewis lung cancer cells and BCG (12.5mg/kg). The dynamic changes of tumor volume were observed. The changes of number of CD4+CD25+ Treg and the expression of Foxp3 in spleen were detected by flow cytometer and semi-quantitative RT-PCR. The changes of T lymphocyte proliferation and killing function spleen were detected. Results The tumor volumes grew more slowly in CTX and BCG therapeutic alliance group than in the tumor group. The number of CD4+CD25+ Treg in spleen of mice was lower in therapeutic alliance group than in the tumor group (P<0.05). The expression of Foxp3 mRNA in spleen lymphocyte was significantly lower in therapeutic alliance group than in the tumor group (P<0.05). The changes of T lymphocyte proliferation in spleen were significantly higher in therapeutic alliance group than in the tumor group(P<0.05). The changes of T lymphocyte killing function in spleen was not significantly lower in therapeutic alliance group than in the tumor group (P>0.05). Conclusion After CTX and BCG therapeutic alliance, the number of CD4+CD25+ Treg and the expression of Foxp3 mRNA in spleen of mice with Lewis lung cancer decreased, and enhanced the immune response to tumor, this may delay the growth of the tumor.