The effect of the heparin analog 5-amino-2-naphthalenesulfonate (5-amino-2-NMS) on retinal neovascularization was investigated in the mouse model for oxygen-induced retinopathy (OIR). From postnatal day 7 (P7) until P12, mice were kept in a 75% oxygen environment. On P12, they received an intravitreal injection of 10mM 5-amino-2-NMS in one eye and PBS as control substance in the fellow eye. The animals were intracardially perfused with fluorescein-dextran solution on P17. Retinal whole mounts were prepared and ischemic retinopathy was evaluated in 30 animals using a standardized retinopathy score. A single intravitreal injection of 5-amino-2-NMS reduces significantly angioproliferative changes (blood vessel tufts, extra-retinal neovascularization, and blood vessel tortuosity) compared to the contralateral control eye (p=0.025). The median retinopathy score (maximal 13) for the 5-amino-2-NMS treated eyes was 6 versus 8 for the control eyes. 5-Amino-2-NMS binds to the heparin-binding site of FGF1 and FGF2 and thus may be a promising substance for the local treatment of retinal neovascularization.