Objective:To discuss the expression of B7-H4 protein in breast cancer tissues as well as the relationship among clinical pathological parameters. Methods:Immunohistochemical technique was employed to investigate the expression of B7-H4 in 68 cases of breast cancer and 30 cases of benign fibroadenoma. And statistical analysis was carried out to study the relationship between B7-H4 and pathological parameters. Results:The B7-H4 positive rate of breast cancer was 75%,significantly higher than fibroadenoma tissues (17%)(P < 0.05). And highly expression of B7-H4 was negatively correlated to estrogen receptor (ER) but positively correlated to human epidermal growth factor 2 correlation (HER-2), independent from other factors such as age,size of tumor and clinical stage. Conclusion:Aberrant B7-H4 expression in breast cancer but not benign fibroadenoma implied that B7-H4 may play an important role in the development of breast cancer.