Background and Objective: Evaluation of tumor proliferative activity may provide a predicting parameter to estimate biologic aggression and a subsequent prognosis that has been evaluated in many malignancies. We have selected renal cell carcinoma (RCC) in this study. To determine tumor proliferative activity, KI67 antibody was applied and results were compared with apoptosis, applying P53 antibody and using immunohistochemical staining. Patients and Methods: Specimens of 30 patients who underwent radical nephrectomy for RCC were selected for histopathology and immunohistochemical study. Two different grading systems (S&H, Fuhrman) were used to calibrate average nucleoli diameter and tumor grading on all specimens. After processing of paraffin-embedded samples, they were immunohistochemically stained applying (MIB-1) KI67 monoclonal and P53 antibodies. Then, statistical analysis was done. Results: Tumor grading correlated with the average nucleus diameter. Positive reaction to KI67 and P53 antibodies in tumors increased as compared to control group. No significant relationship between age, sex and tumor grade was obtained. Conclusion: These two antibodies are as easy and reliable markers that could be applied on formalin-fixed tissues for better assessment of the biologic behavior of RCC and probably prediction of patients’ outcome.