The results from the present study demonstrated that niclosamide inhibited the resistance of HER2-positive breast cancer to cisplatin both in vitro and in vivo. Furthermore, niclosamide combined with cisplatin could inhibit breast cancer cell invasion, epithelial-mesenchymal transition and cell stemness. Taken together, the results of the present study suggested that niclosamide combined with cisplatin may be considered as a novel treatment for chemoresistant HER2-positive breast cancer.