Objective: To investigate the effect of carbon nanoparticle suspension injection on sentinel lymph node (SLN) mapping of breast cancer. Methods: Thirty-six patients with breast cancer were subcutaneously injected with carbon nanoparticle suspension into four equal depots around the areola 30 min before surgery. The black stained axillary lymph nodes were found and labeled as SLNs, and then modified radical mastectomy or breast-conserving surgery was performed. Results: SLNs in 34 cases of the entire group were successfully detected and the detection rate was 94.4%(34/36). The accuracy rate and sensitivity was 91.6% (33/36) and 93.3% (14/15), respectively. The false-negative rate was 6.6% (1/15), and there were no false-positive results. Conclusion: Using carbon nanoparticle suspension as a tracer can correctly reveal the status of axillary lymph nodes, and it may provide appropriate guidance on the scope of radical resection for breast cancer.