The dose-dependent cytotoxicity effect on human hepatocyte(HL-7702 cells) induced by "naked" Fe3O4 nanoparticles was assessed through cell viabilities and lactate dehydrogenase(LDH) activities.Three important oxidative indexes of the cells by glutathione peroxidase(GSH-Px),superoxide dismutase(SOD) and malondialdehyde(MDA) were determined.The good correlation of the cell viabilities with their GSH-Px,SOD and MDA levels indicated that the cytotoxicity is related to activation of oxidative stress induced by Fe3O4 nanoparticles.The oxidative stress also leads to corresponding DNA damage in a similar dose-dependent manner,followed by the changes of cell cycle and cell apoptosis.Such work provides important experimental data for the safety evaluation of superparamagnetic Fe3O4 nanoparticles.