Abstract: Abstract: Objective To study the influence of colony stimulating factor-1(CSF-1) and its receptor on cancer cells and immune cells of breast cancer mice and to explore their effects on tumor size, volume and immune system including marrow, thymus, lymphonodus and spleen. Methods 4T1 cell (1×107/PBS) was inoculated in the left subcutaneous of Balb/c mice in order to establish the mice model with breast cancer. Then tumor formation rate, average weight and area change of tumor were measured. CSF-1 and its receptor were injected into experimental mice after tumor was formed, and these mice were killed after observation. The expression of CSF-1 in the spleen of mice was tested by semi-quantitative RT-PCR. The proliferation of T lymphocyte in the spleen and bone marrow were detected by MTT colorimetry. Results After the continuous improvement, tumor formation rate of 4T1 breast cancer was 100% and tumor latency was 7-10 days. After the injection of CSF-1, we found that tumor growth rate of the experimental mice was higher than that of control group. RT-PCR and electrophoresis results revealed that expression of CSF-1 was increased in the spleen of tumor-bearing mice.MTT results showed that the proliferation of immune lymphocytes and tumor cells was increased after CSF-1 treatment. Active proliferation of bone marrow and spleen cells exhibited immunosuppressive phenotype. Conclusion CSF-1 and its receptor could promote the growth of breast cancer tumor in mice.