Abstract: Objective: To study the protein expression of mucin 1 (MUC1) and human epidermal growth factor receptor 2 (HER2) in human breast cancer and to explore the correlation between this expression and the clinicopathologic parameters. Methods: Immunohistochemistry was used to measure the expression of MUC1 and HER2 in 111 breast cancer cases, 37 benign breast tumor cases and 26 normal breast tissue cases. Results: The positive rate of MUC1 and HER2 expression in breast cancer was 83.78% and 46.85%, respectively. The expression of MUC1 and HER2 in breast cancer was signifi-cantly higher than in the normal and benign tissues. Expression of MUC1 was associated with axillary lymph node involvement and clinical stage but not with age, tumor size, histologic grade or pathological typing. The expression of HER2 was associated with the histologic grades and clinical stages of breast cancer but not with age, tumor size, axillary lymph node involvement or pathological typing. MUC1 expression was positively correlated with HER2 expression, r=0.197, P=0.038. Conclusions: Detection of MUC1 and HER2 protein expression can be used to asses the degree of malignancy, axillary lymph node involvement, prognosis and treatment for breast cancer patients.