bjective: To investigate the expressions of breast cancer susceptibility gene 1 (BRCA1) protein and p120-catenin (p120ctn) in invasive ductal carcinoma (IDC) of the breast and their relations with the clinicopathologic characteristics of this tumor, so as to determine their roles in the occurrence and development of IDC and their clinical application values. Methods: The expression of BRCA1 protein and p120ctn in the specimens of IDC, breast adenosis and tumor adjacent breast tissue were detected by immunohistochemical method. The relations of both expressions with the various clinicopathologic characteristics of IDC and correlation between the both were analyzed. Results: Among the 60 cases of IDC specimens, the positive expression rates of BRCA1 protein and P120ctn were 60.0% (36/60) and 35.0% (21/60), and both expressions were significantly lower than those in the breast adenosis and tumor adjacent breast tissues, respectively (all P<0.05). The expression status of BRCA1 protein was related to high incidence age, clinical stage, presence of axillary lymph node metastases and histological grade of the patients (all P<0.05), but unrelated to their tumor size (P>0.05). The expression status of p120ctn was relevant to the clinical stage, presence of axillary lymph node metastases and histological grade of the patients (all P<0.05), but irrelevant to their age at onset of disease and tumor size (both P>0.05). There was a positive correlation between the expression of BRCA1 protein and p120ctn in IDC tissues (r=0.314, P<0.05). Conclusion: The combination detection of BRCA1 protein and p120ctn can be used for diagnosis and determination of the degree of malignancy and prognosis of IDC, and provide a basis for the individualized treatment of IDC patients.