Abstract: Objective: To investigate the difference of endothelial cell in ultrastructure、markers and permeability between blood-brain barrier and blood-optic nerve barrier.Methods: Twenty normal male SD rats′ optic nerve（prelaminar region,lamina cribrosa,retro-laminar region,intraorbital portion,intracanalicular portion,intracranial portion） and cerebral cortex were removed separately.Ultrastructure of endothelial cell was observed by electron microscopy.Employing immunohistochemical staining the relative distribution was determined for the OX-26 and extravasated fibrinogen around microvessels.Results: Prelaminar region had a significantly higher number of plasmalemmal vesicles than that of cerebral cortex（P＜0.05）;Microvessels in the prelaminar region showed no expression of the OX-26.but fibrinogen was positive around microvessels.Conclusions: Microvessels in prelaminar region lack the typical blood-brain barrier characteristics.