Abstract: Objective To explore expression of KAI1 gene and its relationship with micrometastases in removed axillary lymph nodes in stage I breast cancer patients.Methods Carcinoma tissuses and paraffin blocks of 840 surgically removed lymph nodes from 56 cases of stage I breast cancer with no lymph nodes involved by routine pathology were re-examined by immunohistochemical staining, using monoclonal anti-KAI1 and anti-EMA respectively.Results Micrometastases was observed in 12 of 56 patients examined(21.4%).The positive rate of KAI1 in breast cancer tissue was 32.1%(18/56).KAI1 expression rate was 75.0% in non-invasive group and 25.0% in invasive group respectively, with significant difference.The positive rate of KAI1 was 8.3% in the positive group of micrometastases and 38.6% in the negative group, with significant difference.Conclusion The low KAI1 expression was detected in the early stage of breast cancer with micrometastases and associated with invasive potential.KAI1 gene could be used as an index to evaluate the metastases of breast cancer at early stage.