Breast cancer (BC) is a multifactorial disease and is prone to drug resistance during treatment. In this study, we described a new class of multifunctional estrogen receptor (ER) modulators ground on a prerogative indirect antagonism skeleton (OBHS, oxabicycloheptene sulfonate) of ER containing a phenylselenyl group. Compound <b>34b</b> showed significant antiproliferative activities against tamoxifen-sensitive (MCF-7) and -resistant (LCC2) cells. Moreover, hexokinase 1 (HK1) was identified as a direct target of <b>34b</b>. Further mechanism investigations proved that <b>34b</b> induced apoptosis, which was associated with mitochondrial dysfunction caused by the synergistic effects of downregulating mitochondrial-bound HK1 protein and promoting reactive oxygen species generation. <i>In vivo</i>, <b>34b</b> had a favorable pharmacokinetic profile with a bioavailability of 23.20% and exhibited more potent tumor suppression than tamoxifen both in MCF-7 and LCC2 tumor xenograft models. Collectively, our studies showed that <b>34b</b> is a promising new multifunctional candidate compound for ERα<sup>+</sup> BC treatment, particularly for tamoxifen-resistant BC.