Object To investigate the in vivo antioxidant effect of the extract from Rosmarinus officinalis L. and its active substances. Methods The contents of MDA, the activites of SOD and GSH Px in serum, heart, liver, brain and skeleton muscle were determined in oxidative stress mouse model caused by exercise. Results It was found that in serum, liver, heart and skeleton muscle except the brain, the contents of MDA were decreased and the activities of SOD and GSH Px were increased by 250 mg/kg and 500 mg/kg of total phenolic diterpenes (TPD) extract taken. Conclusion The results showed that R. officinalis has prominent antioxidant effect in exercise mice and the active constituents may be phenolic diterpenes.