Objective：To investigate the expressions and clinical significances of estrogen receptor（ER），progesterone receptor（PR），human epidermal growth factor receptor-2（HER-2） and cell proliferative nuclear antigen Ki67 in human medullary carcinoma of the breast. Methods：The pathological data of 43 cases of medullary breast carcinoma（MBC） were collected. The expressions of ER，PR，HER-2 and Ki67 in carcinoma tissues in 43 cases were detected by immunohistochemical S-P method. Another 120 cases of invasive ductal carcinoma（IDC） of the breast were chosen as the controls. Results：The positive expression rates of ER，PR，HER-2 and Ki67 in MBC tissues were 8/43（18.75%），11/43（25.58%），14/43（32.56%），7/43（16.28%），respectively；meanwhile，the positive rates in IDC were 25/120（20.83%），33/120（27.50%），49/120 （40.83%），42/120（35.00%），respectively. The positive rate of Ki67 in IDC was significantly higher than that in MBC（P<0.05）. The positive expression of Ki67 was associated with tumor volume and lymph node metastasis（P<0.05），but not correlated with the age and clinical stage. There was a positive relationship between the expression of Ki67 and HER-2（r=0.447，P<0.05） and there was no relationship between the expression of Ki67 and PR and PR（r=0.113 and r=1.129，P >0.05）. Conclusions：The expression of Ki67 is correlated with the genesis，development of breast cancer，which can be con－sidered as a biological indicator in MBC. It will be useful for the prognosis through detecting the expression of Ki67 combined with ER，PR and HER-2.