Background Oxidative stress plays an important role in the pathogenesis of epidermal diseases. This study aimed to investigate the effects of quercetin on the anti-oxidative response and on mitochondrial protection in cultured normal human keratinocytes. Methods Cultured HaCaT cells were treated with different concentrations of H_2O_2 (0, 50, 100, 250, 500 μmol/L) for different periods of time (0.5, 1,2,4 hours) to establish an oxidative stress model. The cultured HaCaT cells were randomly assigned to control, H_2O_2, and quercetin+H_2O_2 groups. For the quercetin groups, the cells were treated with different concentrations of quercetin (0,10, 25, 50 μmol/L) before exposure to H_2O_2. Morphological changes of the cells were observed under an inverted microscope and an electron microscope. The cell viability was detected by the MTT method. The cell apoptosis (AnnexinV/propidium iodide double stain) and mitochondrial membrane potential (△ψm) changes were detected by flow cytometry. Results An oxidative stress model of HaCaT cells was established under a suitable concentration (250 μmol/L) and treated time of H_2O_2 (2 hours). The cell viability and △ψm decreased in a concentration-dependent and time-dependent manner while the percentage of apoptotic cells significantly increased in the H_2O_2 groups compared with the control group (P