Objective  To investigate the effect of plateau hypoxia on the blood-brain barrier after subarachnoid hemorrhage (SAH) in rats.   Methods  Adult male SD rats (n=78) were randomly divided into 4 groups: sham group (sham), SAH model group (SAH), plateau hypoxia sham group (Hp sham) and plateau hypoxia SAH model group (Hp SAH). The rat model of plateau hypoxia was established through low-pressure simulation chamber (altitude 5000 m), and the SAH model was established by endovascular perforation method. At 24 hours after SAH, neurobehavior score and SAH grade were assessed. The morphological changes of neurons and apoptosis of nerve cells in the CA1 region of hippocampal were observed by the staining of Nissl and TUNEL. The expression of phosphorylated PI3K (p-PI3K), PI3K, phosphorylated Akt (p-Akt), Akt, phosphorylated nuclear factor κB(p-NF-κB), NF-κB, matrix metalloproteinase-9 (MMP-9), occludin and claudin-5 in hippocampal were detected by the method  of Western blotting. The expression of occludin and claudin-5 proteins in the CA1 region of hippocampal were observed by immunofluorescent staining.    Results  At 24 hours after SAH, the neurobehavior score decreased significantly and SAH grade increased significantly in the SAH and Hp SAH group (P <0.05). Neurobehavior score decreased significantly in the Hp SAH group compared with the SAH group (P< 0.05). In the SAH group, neurons in the CA1 region of hippocampus were atrophied and deformed, the arrangement were disordered, the number of neurons decreased significantly, and the apoptosis of nerve cells increased significantly(P< 0.05). Plateau hypoxia could aggravate the morphological damage of neurons and apoptosis of nerve cells. The expression of p-PI3K/PI3K, p-Akt/Akt, occludin and claudin-5 proteins decreased significantly, while the expression of p-NF-κB/NF-κB and MMP-9 proteins increased significantly in the SAH and Hp SAH group (P< 0.05). The expression of p-PI3K/PI3K and MMP-9 proteins increased significantly in Hp SAH group compared with the SAH group. The expression of claudin-5 protein increased significantly in Hp sham group compared with the sham group (P<0.05). Immunofluorescent staining showed that the expression of occludin and claudin-5 proteins in the CA1 region of hippocampus decreased in the SAH group. Plateau hypoxia could further decreased the expression of occludin and claudin-5 proteins. Conclusion  Plateau hypoxia aggravates blood-brain barrier disruption after subarachnoid hemorrhage in rats through inhibiting PI3K/Akt/NF-κB pathway.