Inactivation of tumor suppressor genes may play an important role in many human cancers including breast. This study was done to determine the relationship between the expression of p53 and Rb protein and prognostic factors such as histopathologic differentiation, tumor size, and lymph node metastasis. In 57 cases of breast invasive ductal carcinomas, the immunohistochemical staining with p53 and Rb protein gave the following results: p53 protein was detected in 45.6% (26/57) of cases. Tumors with large size, poor differentiation or lymph node metastases tended to show increased expression of p53 protein. However, p53 protein expression did not show any significant correlation with prognostic factors such as tumor size (p value 0.25), histologic grade (p value 0.75), and positive lymph node status (p value 0.26). Rb protein was detected in 57.9% (33/57) of cases. Rb protein also did not show any significant correlation with prognostic factors such as tumor size (p value 0.56), histologic grade (p value 0.71), and positive lymph node status (p value 0.98). There was no significant correlation between p53 expression and Rb protein expression (p value 0.80).