Abstract: OBJECTIVE To understand the effect and significance of extract of Cordyceps Sinensis on mice with viral myocarditis. METHOD 100 male BALB/c mice were randomly divided into a control group,an infection group and a group treated with extract of Cordyceps Sinensis.The mice in the infection group and the group treated with extract of Cordyceps Sinensis were inoculated with Coxsackie B3 virus and were then killed seven and fourteen days respectively after the inoculation.Myocardium SOD,MDA and iNOS expressions were determined and semiquantitative scoring of the pathological changes of the heart was carried out under the optical microscope. RESULT Compared with the infection group,SOD activity and iNOS expressions in the group treated with extract of Cordyceps Sinensis increased markedly(P<0.01),MDA level decreased(P<0.01) and myocarditis was relieved.CONCLUSION Extract of Cordyceps Sinensis can alleviate lipid peroxidation of mice myocardium by increasing active antioxidase and inducing iNOS expression.