Cancer stem cells (CSC) are defined as a small population of cells in tumor that are responsible for the tumor initiation, resistance and recurrence. Chemo-resistance remains to be one of the major obstacles in conventional chemotherapies. One of the reasons that majority of chemotherapeutics are not effective in eradicating cancer cells is due to the existence of CSC, which are usually in a non-proliferative or dormant state. In this paper, we hypothesized that in order to improve the outcome of conventional chemotherapy, it will be more effective to utilize CSC stimulating factors in combination with conventional chemotherapeutics. The current study aimed to investigate the feasibility of using prolactin (PRL), a hormone intimately involved in mammary gland development, in combination with cisplatin as an alternative to target breast CSC (BCSC). Using tumorsphere formation assay we demonstrated that PRL was able to alter the cancer cell proliferation pattern in tumorspheres, which accompanied with increased CD44+24cell population. We further showed that PRL treatment reduced the ability of breast cancer cells to form tumorspheres. Moreover, PRL significantly enhanced cisplatin's inhibitory effects in tumorsphere formation. The IC 50 value of cisplatin was reduced by more than half with the addition of PRL in tumorsphere formation assay. The efficacy of this combinational approach was further confirmed through in vivo experiments (McNeu A allograft tumor growth and 4T1 total survival rate). Finally, PRL and cisplatin combination treatment significantly delayed naturally developed breast tumor growth in neutransgenic mice. Taken together, our study provided evidence to support the hypothesis that the addition of PRL to conventional chemotherapy (cisplatin) may be an effective alternative to target BCSC.