Purpose:To detect the expression of MDR 1 / P-gp,C-erbB-2 in breast cancer and study the correlation between MDR 1 /P-gp and C-erbB-2. Methods:Expression of MDR 1 gene was measured with the flu orogenic quantitative RT-PCR method in 57 cases of breast cancer and 20 cases o f control group (including 10 cases of benign breast lesions and 10 cases of adj acent breast tissues). In addition, immunohistochemical analyses was used to det ect the expression of P-gp and C-erbB-2 protein in the above mentioned tissu es. Results:The amplification rate of MDR 1 gene and the expre ssion of P-gp protein in breast cancer group was 50.88% (29/57) and 42.11% (24/ 57), which had a significient difference as compared to the control group. The a mplification of MDR 1 gene were higher than the expression of P-gp protein ,there was close correlation between them but not complete correspondence.The p ositive rate was 28.07%(16/57) in detecting the overexpression of C-erbB-2 pro tein in breast cancer group, nevertheless, no positive case was found in the con trol group. The expression of MDR 1/P-gp was also correlated with the over expression of C-erbB-2. Conclusions:Multidrug resistance gene1(MDR 1)and protoonco gene C-erbB-2 were co-expressed in breast cancer,and their expression were po sitively related. The expression of above mentioned two genes have a relationshi p with multidrug resistance in breast cancer.