Objective:To investigate the protective effect and mechanism of hydrogen sulfide (H2S) on hydrogen peroxide(H2O2)-induced injury in isolated thoracic aorta of rats. Methods:Thoracic aortic rings were isolated from normal Sprague-Dawley rats,subsequently exposed to 300 μmol/L H2O2 to establish an oxidative stress model. The thoracic aortic rings were pre-treated with 25 μmol/L,50 μmol/L or 100 μmol/L of NaHS followed by incubation with 300 μmol/L H2O2. The endothelium-dependent vasorelaxant function of thoracic aortic rings was measured by a pressure transducer coupled to a Labchart V6 System. Production of ROS was evaluated using DHE fluorescent staining assay. The expressions of protein MAPK/ERK1/2 and p-ERK1/2 in thoracic aortic were determined by Western blot analysis. Results:H2O2 of 300 μmol/L can decrease vasorelaxant function in rats’ thoracic aortic rings. Pre-treated with 50 μmol/L or 100 μmol/L of NaHS can attenuate the damage and decrease the production of ROS caused by H2O2. H2O2 also activated MAPK/ERK pathway in the isolated rats’ thoracic aorta,which could be inhibited by NaHS of 50 μmol/L or 100 μmol/L. Conclusion:H2S may have protective effect against H2O2-induced injury through ERK signal pathway in isolated thoracic aorta of rats.