Interleukin 38 (IL-38) is a novel identified cytokine of IL-1 family in which some members are important in inflammation and angiogenesis. However, the role of IL-38 in regulating angiogenesis is unknown. The aim of the present study is to explore the effect of IL-38 on angiogenesis. Oxygen-induced retinopathy (OIR) of C57BL/6 J mice was induced by exposure of hyperoxia (75% oxygen) from postnatal day 7 (P7) to P12 and then returned to room air. The mice were injected with IL-38. At P17, neovascular region (tufts) and avascular area of the retinas were analyzed. The data showed that administration of IL-38 in vivo inhibited retinal angiogenesis significantly. Furthermore, the addition of IL-38 to the cell cultures attenuated the proliferation, scratch wound healing and tube formation of vascular endothelial cells induced by VEGF significantly. Our findings suggest that IL-38 is an antiangiogenic cytokine in pathophysiological settings and may have therapeutic potential for angiogenesis related diseases.