Granulocyte colony-stimulating factor (G-CSF) is a known hematopoietic glycoprotein, and recent studies have revealed that G-CSF possesses other interesting properties. Oxidative stress is involved in many diseases, such as atherosclerosis, heart failure, myocardial infarction, Alzheimer disease, and diabetic retinopathy. This study was designed to examine whether G-CSF has a protective effect on endothelial cells against oxidative stress and to investigate whether G-CSF has a therapeutic role in ischemic vascular diseases. Expression of G-CSF (P < .01) and G-CSF receptor (P < .05) mRNA in human retinal endothelial cells (HRECs) was significantly up-regulated by oxidative stress. Treatment with 100 ng/mL G-CSF significantly reduced H(2)O(2)-induced apoptosis in HRECs from 61.7% to 41.4% (P < .05). Akt was phosphorylated in HRECs by G-CSF addition, and LY294002, a PI3K inhibitor, significantly attenuated the antiapoptotic effect of G-CSF (by 44.1%, P < .05). The rescue effect was also observed in human umbilical vein endothelial cells. In mouse oxygen-induced retinopathy model, G-CSF significantly reduced vascular obliteration (P < .01) and neovascular tuft formation (P < .01). G-CSF treatment also clearly rescued the functional and morphologic deterioration of the neural retina. A possibility of a novel therapeutic strategy for ischemic diseases through attenuating vascular regression using G-CSF was proposed.