Background <p>Nanoparticles enable sustained drug release. Infants with retinopathy of prematurity (ROP) treated with Bevacizumab, an anti-vascular endothelial growth factor monoclonal antibody, develop systemic toxicity due to repeat dosing from a short half-life. We optimized fabrication of Bevacizumab nanoparticles in a mouse oxygen-induced retinopathy (OIR) model.</p> Methods <p>Bevacizumab nanoparticle fabrication was optimized for polymer type and ratio, solvent, drug loading capacity (DL) %, and encapsulation efficiency (EE) %. Nanoparticles were characterized using Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). C57BL6/J mice exposed to OIR received intravitreal Empty (<i>n</i> = 18), Bevacizumab-loaded nanoparticles (<i>n</i> = 18), or Free Bevacizumab (<i>n</i> = 12) at P13 to right eyes. Fluorescein Angiography (FA) was performed at P20. Retinal avascular area, arterial tortuosity, and vein width were quantified.</p> Results <p>SEM showed spherical nanospheres. TEM and FTIR confirmed drugs within nanospheres. DL and EE were optimized at 2.3% and 80%. There was sustained drug release of 80% at 72 h. FA showed increased retinal avascular area, reduced retinal artery tortuosity, and retinal vein width in Bevacizumab nanoparticle treated right eyes.</p> Conclusions <p>Intravitreal administration of Bevacizumab-loaded nanoparticles significantly improved retinal vasculopathy in mice with OIR, without repeat dosing. Further toxicity studies are needed before clinical translation.</p> Impact <p><UnorderedList Mark="Bullet"> <ItemContent> <p>Retinopathy of Prematurity is treated with anti-vascular endothelial growth factor drugs such as Bevacizumab.</p> </ItemContent> <ItemContent> <p>Anti-VEGF drugs result in systemic toxicity from repeat dosing due to their short half-life.</p> </ItemContent> <ItemContent> <p>We, for the first time, show the feasibility and optimization of nanoparticle formulation of bevacizumab in a mouse model of ROP.</p> </ItemContent> <ItemContent> <p>Intravitreal Bevacizumab nanoparticles may prevent systemic toxicity and improve outcomes in infants with ROP.</p> </ItemContent> </UnorderedList></p>