Mitochondria play a central role in biological oxidation that inevitably generates reactive oxygen species (ROS) as by-products. Maintenance of mitochondrial redox balance status requires NADPH, which is primarily generated by the mitochondrial matrix protein isocitrate dehydrogenase 2 (IDH2). The activity of IDH2 is regulated by post-translational modifications (PTMs). In this study, we found IDH2 is modified by small ubiquitin-like modifier 1 (SUMO1) at lysine 45. SUMO specific protease 1 (SENP1) is responsible for deSUMOylation of IDH2. SUMOylation of IDH2 is induced by oxidants and enhances the antioxidant activity of IDH2 to protect cells against oxidative stress. Mutation of the SUMOylation site impairs the enzymatic activity of IDH2 and hence decreases levels of alpha-ketoglutarate (alpha-KG), NADPH and GSH. Cells with SUMOylation deficient IDH2 suffer more apoptosis than that with wild type IDH2 under oxidative stress. These results indicate that SUMOylation is an important way to regulate IDH2 activity to maintain mitochondrial redox balance. (C) 2020 Elsevier Inc. All rights reserved.