Abstract: Objective To explore the pathogenesis of arsenism and search the useful clinical enzymological indices of arsenism,the changes of the serum enzymes correlating to the damage of hepatic cells and hepatic mitochondria were studied in chronic arsenism rats.Methods 75 mg/L arsenic trioxide was administered to Wistar rats through drinking water for 6 months.Hepatic mitochondria was extracted by differential velocity centrifugation.The activities of respiratory enzymes of hepatic mitochondria and the serum enzymes were determined by spectrophotometer.Results The activities of hepatic mito-chondria cytochrom C oxidase and A TPase were decreased,and the serum activities of glutammate dehydrogenase,ornithine carbamoyl transferase,adenosine deaminase,argininase,glutathione-S-tranferase increased in arsenism rats.Conclusion The chronic arsenism could result in the activity decline of the mitochondria cytochrome C oxidase and A TPase.The incremental activities of serum enzymes which are relative to the fumction of hepatic cell and mitochondria further demonstrate the damage to hepatic cell and its mitochondria from arsenism.The determinations of the activities of five enzymes above are with some values to the assistant diagnoses of chronic arsenism.