A key initiator in the development of diabetic retinopathy is considered to be the production of reactive oxygen species (ROS) in the retinal mitochondria, and their scavenging enzyme, manganese superoxide dismutase (MnSOD), is compromised. However, the mechanism by which high glucose regulates MnSOD is unclear. In this study, we found that a high concentration of glucose inhibited the expression of the histone deacetylase SIRT3, which resulted in a reduction in MnSOD activity in bovine retinal capillary endothelial cells and in the retinas of diabetic rats. Conversely, SIRT3 overexpression attenuated hyperglycemic stress through deacetylation and activation of MnSOD. Furthermore, the hyperglycemia-induced downregulation of SIRT3 involved the activation of poly (ADP-ribose) polymerase (PARP). Our study is the first to link the deacetylation of MnSOD by PARP-regulated SIRT3 with the pathogenesis of diabetic retinopathy. Understanding the role of SIRT3 in the pathogenesis of diabetic retinopathy could help elucidate key molecular targets for future pharmacological interventions.