Abstract: Objective To observe the damage of sodium selenite on cultured cortical neurons and its mechanism.Methods Sodium selenite was added to neuronal after two days cultured in vitro with different concentrations(0.000,0.004,0.020,0.100,and 0.500 Lmol/L).Mitochondr ial membrane potential(confocal microscopy throug h focusing,CMTF)and MTT were performed to investigate the alterations of mitochondrial structure and functions;DNA damage was measured by single cell gel electrophoresis(SCG E).Each experiment was repeated at least 3 times.Results High concentration of sodium selenite(0.100~0.500μmol/L)could cause significant damage of cultured cortical neurons,whereas low concentration of sodium selenite(0~0.020μmol/L)had no effect on the activity of the cells.Conclusion Our data demonstrated that high concentration of sodium selenite could damage the cultured neurons.The alterations of mitochondrial structure and functions and DN A damage played important roles in neurotox ic mechanism induced by sodium selenite.