ackground: The involvement of apoptotic genes in tumor genesis is well recognized. It was reported that P53 to be expressed more frequent in invasive thymoma than thymoma and expression of bcl-2 is positively correlate with aggressiveness of thymic epithelial neoplasm. We aimed to assess the expression of P53, bcl-2, and Rb genes related protein in thymoma and invasive thymoma. Materials and Methods: We analyzed formalin-fixed paraffin embedded tissue sections of thymic epithelial tumor during 1999 to 2001 for P53, bcl-2, and Rb protein by Immunohistochemistry. Results: Fifteen cases of thymic epithelial tumor including nine thymoma and six invasive thymoma were collected. P53 nuclear staining were found in epithelial cells of 14 cases (8 thymoma and 6 invasive thymoma). Rb protein was present in 10 cases (5 thymoma and 5 invasive thymoma). Cytoplasmic staining for bcl-2 was positive in six cases, of these, two were invasive. Conclusion: Between Products of these three genes, P53 protein accumulation is more pronounced than other two, and there is inverse relationship between P53 and bcl-2 expression. The accumulation of P53, bcl-2, and Rb does not correlate with invasiveness of tumor. We may suggest that difference in expression of P53, in our study, may occur in the absence of mutation due to some ethnic or environmental factors which needs more investigation. We also suggest that organotypical differentiation present at the molecular level in Thymoma. (Tanaffos 2003; 2(5): 7-14)