We studied the expression of MDM2 protein and p53 protein in 67 cases of the breast carcinoma. The result demonstrated no significant relationship between the MDM2 protein expression and any of the clinicopathological parameters except for the estrogen receptor status (p=0.033). Furthermore, in p53 protein negative cases, there was a significant relationship between MDM2 protein expression and the ER status (p=0.027). This study showed the expression of ER to be associated with MDM2 protein in p53 protein negative breast carcinoma. These results thus suggested that an investigation of both p53 and MDM2 gene alteration revealed precise information regarding breast carcinoma.