Estrogen enhances mitochondrial function by enhancing mitochondrial biogenesis and sustaining mitochondrial energy–transducing capacity. Shifts in mitochondrial bioenergetic pathways from oxidative phosphorylation to glycolysis have been hypothesized to be involved in estrogen‐induced tumorigenesis. Studies have shown that mitochondria are an important target of estrogen. Estrogen receptor‐β (ERβ) has been shown to localize to mitochondria in a ligand‐dependent or ‐independent manner and can affect mitochondrial bioenergetics and anti‐apoptotic signaling. However, the functional role of mitochondrial ERβ in tumorigenesis remains unclear. Clinical studies of ERβ‐related tumorigenesis have shown that ERβ stimulates mitochondrial metabolism to meet the high energy demands of processes such as cell proliferation, cell survival, and transformation. Thus, in elucidating the precise role of mitochondrial ERβ in cell transformation and tumorigenesis, it will be particularly valuable to explore new approaches for the development of medical treatments targeting mitochondrial ERβ–mediated mitochondrial function and preventing apoptosis.