Objective：To investigate the expression of B7 homolog 4（B7-H4） in human breast cancer and to analyze its relationship with number of tumor-infiltrating FOXP3+ Tregs and cancer lymphonode metastasis. Methods：B7-H4 expression was detected by im－munohistochemistry in 16 cases of normal breast tissues and 79 cases of breast cancer. Number of tumor-infiltrating CD3+ T cells and FOXP3+ Tregs was determined by indirect immunofluorescent double-staining in 64 cases of invasive breast cancer. Correlation be－tween B7-H4 expression and number of tumor-infiltrating CD3+ T cells and FOXP3+ Tregs as well as lymphonode metastasis was analyzed. Results：B7-H4 expressed in 6.3% normal breast tissues，40.0% ductal cancer in situ and 78.1% invasive breast cancer. B7-H4 expression in invasive breast cancer was significantly higher than that in normal breast tissues and ductal cancer in situ（P=0.000，P=0.009） without significantly difference between normal breast tissues and ductal cancer in situ（P=0.037）. Intensity of B7-H4 was positively correlated with number of infiltrating FOXP3+ Tregs（rs=0.368，P=0.003） but was negatively correlated with number of infiltrating CD3+ T cells（rs=-0.316，P=0.011） and had no relationship with lymphonode metastasis of breast cancer（P >0.05）. Conclu－sions：B7-H4 overly expresses in breast cancer. B7-H4 is in association with the local antitumor immune inhibition not lymphonode metastasis of tumors.