Abstract： Objective To investigate the expression of anti-oncogene P53 and cancergeneMDM2 proteins and their significance inthe pathogenesis and progress of Breast tumor. Methods To detect the expression ofP53 andMDM2 in 60 cases of Breast tumor and 20 cases of normal Breast tissue with immunoh is to chemical method. Results The positive rate of P53 in the tissues of the 60 cases of breast tumor is much higher than it in the 20 cases of normal breast tissues. There is statistical significance in the disparity (P ＜ 0. 01). Mdm2, P53protein expression and tumor size was no difference (P ＞ 0. 05) , clinical stage, axillary lymph node metastasis was significant difference(P ＜ 0. 01). Conclusion Both P53 andMDM2 participate in the pathogenesis and progress of breast tumor and they can be considered as the biological index to evaluate breast tumor.