The present study provided the first systematic identification of DMS as a catalytic antioxidant to protect cells and extend lifespan via the peroxidase activity of MsrA. After binding to the catalytic pocket of MsrA and forming of a positively charged sulfonium intermediate, DMS scavenged harmful radicals, reduced oxidative stress in the cell model, and mediated longevity. Considering the existence of DMS in the organisms is conserved, including C. elegans, Drosophila, mouse, rat, and human, DMS may act as a new member in the family of the physiologic antioxidative molecules.