Angiogenesis is a critical biologic process in the development of Retinopathy of Prematurity (ROP), the leading cause of blindness in the very low birth weight infant. We investigated the effectiveness of squalamine, a natural aminosterol inhibitor of angiogenesis isolated from the dogfish shark, in an oxygen induced model of retinopathy. C57BL/6J mice were exposed to 75% oxygen from postnatal day 7 to 12, returned to room air and sacrificed at postnatal day 17. Control mice were raised in room air and sacrificed at postnatal day 17. Oxygen exposed animals received squalamine (40 mg/kg SQ daily) from postnatal day 12 to 17 (n=8) or no treatment (n=12). Control animals similarily received squalmine (n=6) from postnatal day 12 to 17 or no treatment (n=14). Analysis of retinae following fluorescein conjugated dextran angiography was performed on postnatal day 17 and the degree of retinopathy was scored using a retinal scoring system which assessed blood vessel growth inhibition, tuft formation, extraretinal neovascularization, degree of central vasoconstriction, and the presence of retinal hemorrhages and plus disease. Oxygen exposed animals had a higher retinopathy score, 7.6 ± 1.8, than control animals, 1.5 ± 0.6 (p<0.001). Squalamine administration inhibited oxygen indued retinopathy, score of 4.1 ± 1.6 (p<0.001), with no effect in control animals, score of 0.7 ± 0.2. In oxygen exposed mice, squalamine significantly inhibited blood vessel tuft formation, extraretinal neovascularization, and retinal hemorrhage and plus disease. Squalamine had no effect on blood vessel growth inhibition or central vasoconstriction; both presumibly due to the hyperoxia exposure which preceded squalamine administration. Squalamine administration had no adverse effects in control mice. In conclusion, squalamine inhibited the development of retinal neovascularization in an oxygen induced mouse model of retinopathy and had no adverse effects on normal retinal blood vessel growth. We speculate that squalamine acts specifically on mitogen induced proliferation of endothelial cells and may ultimately provide a therapeutic alternative for progressing ROP. Funded in part by NIH EY00330.