RY10-4, an anti-tumor agent, exerts cytotoxicity to various human cancer cell lines. However, few studies reported the effect of combined application of RY10-4 and chemotherapeutic drugs against cancer cells with multidrug resistance (MDR). In this study, P-glycoprotein (P-gp), which is reported to mediate MDR to anti-cancer drugs, was proved to be overexpressed in the adriamycin (ADR)-resistant human breast cancer cells, namely MCF-7/ADR cells. Furthermore, RY10-4 application resulted in a downregulation of P-gp in MCF-7/ADR cells, thus leading to higher chemosensitivity to ADR. Our study further demonstrated that the MDR phenomenon was under the control of the PI3K/Akt/NF-κB pathway, which was suppressed by RY10-4, leading to MDR reversal effects in MCF-7/ADR cells. In vivo, MCF-7/ADR cells were effectively suppressed by the combined ADR/RY10-4 treatment compared with the ADR-alone treatment. Taken together, these results demonstrated that RY10-4 reverses the MDR phenotype in MCF-7/ADR cells by suppressing the PI3K/Akt/NF-κB pathway.