Abstract： Objective To observe the effect on succinate dehydrogenase (SDH) of mitochondria in myocardium and liver in sepsis rats treated with edaravone. Methods 30 Sprague-Dawley rats were divided into 3 groups: sham operated group ( group A ), controlled operated group ( group B ), treated group with edaravone (group C). The model of sepsis rats was made by the way of caecum ligated and punctured and 20mg/kg lactate levofloxacin was subcutaneously injected (sci) 15min before and 3h after operation in three group. 5mg/kg edaravone were sci 15min before and 3h after operation in group C. Liver and myocardium were taken from all of them 18h after operation. The activities of SDH in myocardial and hepatic mitochondria were detected, pathological change of mitochondria in liver and myocardium were observed. Results The activities of SDH in myocardial and hepatic mitochondria in group B [ (0. 21 ± 0. 07 ) U/mgprot, (0. 23± 0. 08 ) U/mgprot ] were significantly decreased compared with group A [ ( 0. 33 ± 0. 10 ) U/mgprot, ( 0. 38±0. 12)U/mgprot]. The activities of those in group C[ (0.31 ±0. 08) U/mgprot, (0. 36 ±0. 11)U/mgprot] were significantly increased than group B. Myocardial and hepatic mitochondria swelling and endocytoplasmic reticulum expanding were found in group B by electron microscope, while it showed normal in group C. Conclusion Hepatic and myocardial mitochondrial structure were destroyed and activities of SDH were decreased in sepsis rats. They could be effectively protected by edaravone.