OBJECTIVE: To explore the effects of adenovirus-mediated wild-type p53 gene (Ad-p53) on the reversal of multidrug resistance (MDR) and multidrug resistance gene-1 (MDR1) in adriamycin (ADM) resistant human breast cancer cell. METHODS: Ad-p53 was transfected into the human breast cancer cells of the line MCF-7/ADM. p53 protein expression was detected by flow cytometry (FCM). The cell proliferation was assessed by trypan blue dye exclusion. The effects of Ad-p53 on ADM mediated drug resistance were observed by MTT assay. The expression levels of MDR1 mRNA were detected with real-time RT-PCR. RESULTS: The expression rate of p53 protein of the MCF-7/ADM cell was increased from 10.24% to 36.20% after transfected by MOI(50) Ad-p53 for 48 hours. The growth inhibition rate was 7.4 % (P = 0.003). The chemosensitivity of MCF-7/ADM to ADM increased by 11.6 times (P = 0.001). The result of real-time RT-PCR reveales that MDR1 mRNA was decreased from 1.25 +/- 0.01 to 0.91 +/- 0.01 (P = 0.011) after the MCF-7/ADM cells were transfected by Ad-p53. CONCLUSION: Ad-p53 can inhibit the expression of MDR1 gene and partially reverse the MDR of MCF-7/ADM cells, thus enhancing the chemosensitivity of human breast cancer cells to ADM.