Yes / Multidrug resistance (MDR) limits the beneficial outcomes of conventional breast cancer chemotherapy. Ras-related nuclear protein (Ran-GTP) plays a key role in these resistance mechanisms, assisting cancer cells to repair damage to DNA. Herein, we investigate the co-delivery of Ran-RCC1 inhibitory peptide (RAN-IP) and doxorubicin (DOX) to breast cancer cells using liposomal nanocarriers. A liposomal delivery system, co-encapsulating DOX, and RAN-IP, was prepared using a thin-film rehydration technique. Dual-loaded liposomes were optimized by systematic modification of formulation variables. Real-Time-Polymerase Chain Reaction was used to determine Ran-GTP mRNA expression. In vitro cell lines were used to evaluate the effect of loaded liposomes on the viability of breast and lung cancer cell lines. In vivo testing was performed on a murine Solid Ehrlich Carcinoma model. RAN-IP reversed the Ran-expression-mediated MDR by inhibiting the Ran DNA damage repair function. Co-administration of RAN-IP enhanced sensitivity of DOX in breast cancer cell lines. Finally, liposome-mediated co-delivery with RAN-IP improved the anti-tumor effect of DOX in tumor-bearing mice when compared to single therapy. This study is the first to show the simultaneous delivery of RAN-IP and DOX using liposomes can be synergistic with DOX and lead to tumor regression in vitro and in vivo.