Let-7 microRNAs have been reported to have tumor suppressive functions; however, the effect of Let-7 when used in combination with chemotherapies is uncertain, but may have potential for use in clinical practice. In this study, we used RT-qPCR, western blot analysis, cell proliferation assay, flow cytometry analysis, immunohistochemistry (IHC) staining, luciferase assays, cell sorting analysis and xenografted tumor model to explore the role of Let-7 in the chemotherapy sensitivity of breast cancer stem cells. The findings of the current study indicated that Let‑7 enhances the effects of endocrine therapy potentially by regulating the self‑renewal of cancer stem cells. Let‑7c increased the anticancer functions of tamoxifen and reduced the ratio of cancer stem‑like cells (CSCs), sensitizing cells to therapy-induced repression in an estrogen receptor (ER)‑dependent manner. Notably, Let‑7 decreased the tumor formation ability of estrogen‑treated breast CSCs in vivo and suppressed Wnt signaling, which further consolidated the previously hypothesis that Let‑7 decreases the self‑renewal ability, contributing to reduced tumor formation ability of stem cells. The suppressive effects exerted by Let‑7 on stem‑like cells involved Let‑7c/ER/Wnt signaling, and the functions of Let‑7c exerted with tamoxifen were dependent on ER. Taken together, the findings identified a biochemical and functional link between Let‑7 and endocrine therapy in breast CSCs, which may facilitate clinical treatment in the future using delivery of suppressive Let-7.