Breast cancer is the leading cause of cancer incidence and cancer-related mortality among women and is becoming a major public health problem around the world. The current study aims to investigate the possible role and mechanism of recombinant Apoptin (rApoptin), a potential anticancer candidate that minimally impacts normal cells, in the breast cancer cell proliferation and apoptosis in vitro and in vivo. We found that rApoptin could effectively inhibit the proliferation and apoptosis in MCF-7 and MDA-MB-231 cells in vitro, which was further confirmed by flow cytometry analysis. Apoptin partially inhibited MCF-7 cell xenograft tumor development in vivo. Furthermore, we found via western blot that rApoptininduced apoptosis in MCF-7 and MDA-MB-231 cells was associated with the phosphorylation of Nur77 (p-Nur77) and Akt (p-Akt). In addition, compared with the control groups, rApoptin-treated tissues showed significantly higher expression of Bax and Cyt c while Bcl-2 expression was decreased by rApoptin treatment. Together, our results are the first to demonstrate that rApoptin was able to effectively induce breast cancer cell apoptosis both in vitro and in vivo and that this activity could be regulated by the phosphorylation of Nur77 and Akt and the mitochondrial pathway. Our findings highlight the potential application of rApoptin as a breast cancer treatment. (C) 2018 Elsevier Inc. All rights reserved.