BET inhibitors (BETi) exert an excellent anti-cancer activity in breast cancer. However, the identification of new potential targets to enhance breast cancer sensitivity to BETi is still an enormous challenge. Both NR5A2 and NCOA3 are frequently involved in cancer cells resistance to chemotherapy, also associated with poor prognosis in breast cancer. However, the functions of NR5A2 and NCOA3 in BETi resistance remains unknown. In this study, we found that BETi JQ1 and I-BET151 exhibited anti-cancer effects in breast cancer by inducing ferroptosis. NCOA3 as a coactivator synergized with NR5A2 to prevent BETi-induced ferroptosis. Mechanistically, we identified NR5A2 synergized with NCOA3 to increase expression of NRF2, a transcription factor that controls the expression of many antioxidant genes. Moreover, inhibition of NR5A2 or NCOA3 using small molecule inhibitors enhanced anti-cancer effects of BETi against breast cancer in vivo and in vitro. Altogether, our findings illustrated NR5A2 synergized with NCOA3 to confer breast cancer cells resistance to BETi by induction of NRF2. Inhibition of NR5A2/NCOA3 combined with BETi might be a novel strategy for treatment of breast cancer. (C) 2020 Elsevier Inc. All rights reserved.