Nanoplastics (NPs) may disrupt the blood–brain barrier (BBB), but the underlying cellular routes remain unclear. Here, we tested whether extracellular vesicles (EVs) enhance endothelial uptake, intracellular accumulation, and barrier disruption by polystyrene NPs (PSNPs). Human umbilical vein endothelial cells (HUVECs) were exposed to free PSNPs (100 μg/mL) or PSNP-encapsulated EVs (PSNP-EVs; 1 mg/mL EV protein) for 24 h, with vehicle controls, and barrier function was evaluated in endothelial monolayers using transendothelial electrical resistance (TEER) and permeability assays. Notably, EV encapsulation prolonged intracellular retention of PSNPs and reduced cellular clearance compared with free PSNPs, with signals persisting up to 12 h, whereas free PSNPs peaked at 4 h and declined thereafter. In human endothelial monolayers, PSNP-EVs produced a larger decline in TEER than free PSNPs, resulting in a 2.8-fold greater TEER decline, and promoted macromolecule-permeable paracellular transport, selectively increasing 4-kDa (1.38-fold) and 40-kDa (3.07-fold) dextran permeability while leaving sodium fluorescein largely unchanged. PSNP-EV exposure reduced occludin and ZO-1 expression to 47.6% and 60.8% of control levels, respectively, and disrupted their continuous junctional localization, indicating destabilization of the occludin–ZO-1–actin scaffold. Pharmacologic inhibition of dynamin-mediated endocytosis with dynasore reduced EV uptake by 69.3% and prevented PSNP-EV-induced TEER loss. In vivo imaging further revealed brain accumulation and persistence of administered PSNP-EVs. Collectively, these results indicate that EVs promote sustained accumulation of nanoscale plastics within endothelial cells and the brain, concomitant with increased macromolecular paracellular permeability of the BBB and a heightened neurovascular risk.