Candesartan has been reported to have a protective effect on cerebral ischemia in vivo and in human ischemic stroke. We studied the direct effects of candesartan on blood-brain barrier (BBB) function with our in vitro monolayer model generated using rat brain capillary endothelial cells (RBECs). The in vitro BBB model was subjected to normoxia or 6-h oxygen glucose deprivation (OGD)/24-h reoxygenation, with or without candesartan. 6-h OGD/24-h reoxygenation decreased transendothelial electrical resistance and increased the endothelial permeability for sodium fluorescein in RBEC monolayers. Candesartan (10 nM) improved RBEC barrier dysfunction induced by 6-h OGD/24-h reoxygenation. Immunostaining and immunoblotting analysis indicated that the effect of candesartan on barrier function under 6-h OGD/24-h reoxygenation was not related to the expression levels of tight junction proteins. However, candesartan affected RBEC morphological changes induced by 6-h OGD/24-h reoxygenation. We analyzed oxidative stress and cell viability using chemical reagents. Candesartan improved cell viability following 6-h OGD/24-h reoxygenation, whereas candesartan had no effect on oxidative stress. These results show that candesartan directly improves cell function and viability of brain capillary endothelial cells under OGD/reoxygenation, suggesting that the protective effects of candesartan on ischemic stroke are related to protection of the BBB.