Objective: To explore expressions of multidrug resistance gene (MDR) product P170 and peripheral blood MDR1 mRNA in breast cancer tissue and their clinical significances. Methods: Fluorescent quantitative RT-PCR and immunohis-tochemistry were used to detect peripheral blood MDR1 mRNA before chemotherapy in breast cancer tissue samples from 32 cases with P170 positive (trial group) and 11 cases with P170 negative (control group). Results: There were 14 cases (43.75%) peripheral blood MDR1 mRNA positive and 18 cases (56.25%) negative in 32 cases P170 positive breast cancer patients, while there were 6 cases (54.55%) peripheral blood MDR1 mRNA positive and 5 cases (45.45%) negative in 11 cases P170 negative breast cancer patients; there wasnt a significance difference with peripheral blood MDR1 mRNA express rate in P170 positive (43.75%) group and P170 negative (54.55%) group (x2 = 0.383, P 0.05). There were 12 cases (37.50%) Her-2 positive and 20 cases (62.50%) negative in P170 positive group; there were 2 cases (18.18%) Her-2 positive and 9 cases (81.82%) negative in P170 negative group; there wasnt a significance difference with Her-2 positive rate in P170 positive group (37.50%) and P170 negative (18.18%) group (x2= 1.391, P 0.05). There were 13 cases (40.63%) ER positive and 19 cases (59.37%) negative in P170 positive group; there were 7 cases (63.64%) ER positive and 4 cases (36.36%) negative in P170 negative group; there wasnt a significance difference with ER positive rate in P170 positive group (40.63%) and P170 negative (63.64) group (x2 = 1.742, P 0.05). There were 20 cases (62.50%) PR positive and 12 cases (37.50%) negative in P170 positive group; there were 4 cases (36.36%) PR positive and 7 cases (63.64%) negative in P170 negative group; there wasnt a significance difference with PR positive rate in P170 positive group (62.50%) and P170 negative (36.36%) group (x2 = 2.267, P 0.05). There were 9 cases (28.12%) with lymphaden metastasis and 23 cases (71.88%) without lymphaden metastasis in P170 positive group; there were 5 cases (45.45%) with lymphaden metastasis and 6 cases (54.55%) without lymphaden metastasis in P170 negative group; there wasnt a significance difference with lymphaden metastasis rate in P170 positive group (28.12%) and P170 negative (45.45%) group (x2 = 1.120, P 0.05). Conclusion: 1) There were possibly MDR expressing infrequently in carcinoma tissue and peripheral blood before chemotherapy. 2) FQ-RT-PCR for detecting of peripheral blood MDR1 mRNA is special, sensitive and reliable. It can be used as new molecular biology diagnostic maker dynamic detecting peripheral blood MDR1 mRNA for regulating chemotherapy proposal and elevating chemotherapy effect.