A new diabetic mouse strain, the Akita.PlGF knockout (−/−), was generated to study the role of placental growth factor (PlGF) in the pathogenesis of diabetic retinopathy (DR). PlGF deletion did not affect blood glucose but reduced the body weight of Akita.PlGF−/− mice. Diabetes-induced retinal cell death, capillary degeneration, pericyte loss, and blood-retinal barrier breakdown were prevented in these mice. Protein expression of PlGF was upregulated by diabetes, particularly in vascular cells. Diabetes-induced degradation of ZO-1 and VE-cadherin was reversed due to PlGF deficiency; their expression was correlated with that of sonic hedgehog and angiopoietin-1. PlGF deletion in Akita mice resulted in an increased Akt phosphorylation. Diabetes-activated hypoxia-inducible factor (HIF)1α–vascular endothelial growth factor (VEGF) pathway, including expression of HIF1α, VEGF, VEGFR1–3, and the extent of phospho (p)-VEGFR1, p-VEGFR2, and p–endothelial nitric oxide synthase, was inhibited in the retinas of diabetic PlGF−/− mice. However, expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1, CD11b, and CD18 was not inhibited by PlGF deletion, nor was retinal leukostasis. These results suggest that PlGF is critical for the development of DR, and its genetic deletion protects the retina from diabetic damage. Protective mechanisms are associated with Akt activation and HIF1α-VEGF pathway inhibition, but independent of retinal leukostasis in the retinas of diabetic PlGF−/− mice.