Kaempferol is a dietary flavonoid that is thought to function as a selective estrogen receptor modulator. Estrogen-related receptors alpha and gamma (ERRα and ERRγ) are orphan nuclear receptors that play important roles in mitochondrial biogenesis and cancer development. In the present study, we demonstrated that Kaempferol could functionally antagonize the activities of ERRs based on both response element reporter systems and target gene analysis. We also further confirmed that kaempferol modulated mitochondrial function and suppressed cancer cell growth. These evidences collectively suggest that kaempferol may exert their anti-cancer activities through antagonizing ERRs activities.