Objective:To study the clinical significance of immunocytochemistry(ICC) and reverse transcription-polymerase chain reaction(RT-PCR) in detection of breast cancer micrometastases in bone marrow of breast cancer patients with lymph nodes negative. Methods:After general anesthesia,all patients underwent bone marrow puncture and performed modified radical mastectomy. Bone marrow micrometastases were detected by ICC and RT-PCR in 62 patients, whose axillary lymph nodes showed negative HE-stain. Results:Among the 62 patients,15 cases(24.20%) presented RT-PCR positive,in which 9 cases(14.52%) were also ICC-positive. RT-PCR and ICC showed good uniformity(kappa = 0.6945),and there was significant difference in detective rate between the two methods(χ2 = 4.1667,P = 0.0412). Conclusion:Even there were no axillary lymph nodes involved,micrometastases still could be detected in bone marrow by ICC and RT-PCR. In addition,RT-PCR is more sensitive than ICC.