Abstract: Objective: to study the expression of P²¹.P⁵³ in rectal cancer and its relation to clinical pathological characteristics and the significance of its prognosing rectal cancer. Methods: Using immunohistochemistry (s-p method) P²¹.P⁵³ were studied in 110 cases of rectal the expression of cancer, using normal rectum as controlling group. Results the positive rate of P²¹.P⁵³ oncoprotein was 54.5 %、42.7 %, the expression of P⁵³ had no relation to clinical pathological characteristics of rectal cancer, the cases with expressing P²¹ oncoprotein had lower 3 or 5 year survival rate, worsely differentiated, higher rate of lymph metastasis. Conclusion: P⁵³ gene might be related to rectal. carcinogenisis, P²¹ might be prognosis of rectalcancer.