['It has been demonstrated that platycodin D (PD) exhibits anti-cancer activities. This study aims to investigate the anti-proliferative effects of the combination of PD and doxorubicin (DOX) on human breast cancer cells (MCF-7 and MDA-MB-231 cells).', 'The anti-proliferative effects of different dosages of PD, DOX, and PD\u2009+\u2009DOX on MCF-7 and MDA-MB-231 cells were determined by the MTT assay. The 10\xa0μM PD, 5\xa0μM DOX, and 10\xa0μM PD\u2009+\u20095\xa0μM DOX induced-protein expression of apoptosis-related molecules on MCF-7 and MDA-MB-231 cells were detected by western blot. The 10\xa0μM PD, 5\xa0μM DOX and 10\xa0μM PD\u2009+\u20095\xa0μM DOX-induced mitochondrial membrane potential changes on MCF-7 and MDA-MB-231 cells were stained with JC-1 before visual determination. The intracellular accumulations of DOX, induced by 10\xa0μM PD, 5\xa0μM DOX and 10\xa0μM PD\u2009+\u20095\xa0μM DOX, were detected by flow cytometry.', 'PD enhanced anti-cancer activities of DOX were observed in both MCF-7 and MDA-MB-231 cell lines. Compared with mono treatment, the combined treatment increased the protein expression of cleaved poly (ADP-ribose) polymerase and decreased the mitochondrial membrane potential. The combined treatment with PD did not obviously increase the accumulation of DOX in MCF-7 cells (1.66\u2009±\u20090.13 in DOX-treated group, and 1.69\u2009±\u20090.06 in PD\u2009+\u2009DOX-treated group, P\u2009=\u20090.76), but it significantly increased the accumulation of DOX in MDA-MB-231 cells (1.76\u2009±\u20090.17 in DOX-treated group, 2.09\u2009±\u20090.02 in PD\u2009+\u2009DOX-treated group, P\u2009=\u20090.027).'] Does platycodin D from Platycodonis Radix enhance the anti-proliferative effects of doxorubicin on breast cancer MCF-7 and MDA-MB-231 cells?