Purpose: To investigate the effect of mitochondria-targeted antioxidant peptide SS31 on prevention of high glucose-induced injury on human retinal endothelial cells (HRECs). Methods: Cultured P3-P5 HRECs were divided into three groups: 5 mM glucose group, 30 mM glucose group and 30 mM glucose co-treated with 100 nM SS31 group. 24 and 48 h after treatment, Annexin V-FITC/PI staining was used to evaluate the survival of HRECs. Overproduction of ROS was assessed by MitoSOX staining under confocal microscope. Change of mitochondrial potential (Delta Psi(m)) of HRECs was measured by flow cytometry after JC-1 fluorescent probe staining. Release of cytochrome c was assessed by confocal microscopy and western blot. Expression of caspase-3 and thioredoxin-2 (Trx-2) were measured by western blot and real-time PCR. Results: Compared to the high glucose group, co-treatment with 100 nM 5531 significantly protected HRECs from high glucose-induced injury, reduced the production of ROS in mitochondria, stabilized Delta Psi(m), decreased the release of cytochrome c from mitochondria to cytoplasm, decreased the expression of caspase-3 and increased the expression of Trx-2 in high glucose-treated HRECs. Conclusions: SS31 attenuates the high glucose-induced injuries on HRECs by stabilizing Delta Psi(m), decreasing ROS production, preventing the release of cytochrome c from mitochondria, decreasing the expression of caspase-3 and increasing the expression of Trx-2. Our study suggests that SS31 may be as a potential new treatment for diabetic retinopathy and other oxidative stress-related diseases. (C) 2010 Elsevier Inc. All rights reserved.