Although there are a lot of chemical drugs to treat breast cancer, increasing drug resistance of cancer cells has strongly hindered the effectiveness of chemotherapy. ATP-binding cassette transporters represented by P-glycoprotein (P-gp), multidrug resistance associated protein 1 (MRP1) and breast cancer resistance protein (BCRP) play an important role in drug resistance. This study aims to investigate the effect of 7-O-geranylquercetin (GQ) combining microRNA-451(miR-451) on reversing drug resistance of breast cancer and reveal the mechanism related to P-gp. Real-time RT-PCR and western blot assays showed that miR-326, miR-328, miR-451 and miR-155 inhibitor down-regulated the expression of genes MRP1, BCRP, MDR1 and the corresponding proteins MRP1, BCRP, P-gp, respectively. Cell counting kit-8 (CCK-8) assay indicated that these miRNAs reversed the resistance of MCF-7/ADR cells to Adriamycin (ADR), and miR-451 showed the greatest reversal effect. Combination of GQ and miR-451 enhanced the inhibitory effects of ADR on the proliferation and migration of MCF-7/ADR cells, and attenuated the expression of MDR1 and P-gp in MCF-7/ADR cells. A xenograft tumor model was used to show that GQ and miR-451 amplified the antitumor effect of ADR in nude mice, while western blot and immunohistochemical assays revealed the decreased expression of P-gp in tumor tissues. These results suggest that GQ and miR-451 have synergistic effect on reversing drug resistance through reducing the expression of MDR1 and P-gp in breast cancer MCF-7/ADR cells.