Abstract: Objective To study the effect of cadmium on the structure and function of mitochondria in HEK 293 cell.Methods Mitochondria were isolated from cultured HEK 293 cells and treated with different concentration of CdCl₂.Mitochondr ial permeability transition pore(MPTP)was test ed by spectrophotometer.Morpholo gical changes of mitochondria were observed under transmission electron microscope.Mitochondrial membrane potential(MM P)was monitored by spectrofluor imeter with fluorescence dye Rh-123,and the contents of ROS were detected by spectrofluor imeter with DCFH-DA.The activities of Na⁺-K⁺-ATP ase,Ca²⁺ -Mg²⁺ -ATPase,supero xide dismutase(SOD),glutathione perox idase(GSH-Px) and the contents of malondialdehyde(MDA)were measured.Results MPTP of exposed groups decreased compared with that of the control group,and it can be inhibited by CsA.M itochondria incubated with CdCl₂ were found sw ell under transmission electr on microscope.In the groups of 5,10 Lmol/LCdCl₂,Wm were destro yed(P<0.05)and the contents of ROS increased(P<0.05 and P<0.01).In exposed groups,activities of ATPenzyme,LDH,SOD and GSH-Px declined with the increasing of CdCl₂ concentration(high dose group P<0.01),and the contents of MDA increased(hig h dose group P<0.01).Conclusion CdCl₂ could induce damage of mitochondria,the opening of the MPTP,the decrease of MM P and the increase of ROS,and cause the oxidative stress which is in close relationship with apoptosis.