Objective:To investigate the relationship between Toll-like receptor 9(TLR9)expression of breast cancer cells and their invasion. Methods:After using CpG oligonucleotides to stimulate breast cancer cells,the expression level of TLR9,the viability and invasion of breast cancer cells were examined by Western blot,Transwell and MTT. Results:TLR9 was expressed in MDA-MB-231 and could be promoted by CpG oligonucleotides,but was not in MCF-7. The invasion was enhanced while TLR9 up-regulated. Conclusion:TLR9 plays an important role in the invasion process of breast cancer.