Subarachnoid hemorrhage (SAH)-induced brain injury is highly related to neurological deficits and mortality. Regional cerebral blood flow (rCBF) changes and vasoconstriction are two complications that occur soon after SAH experimentally. In this study we investigated the changes in rCBF and vertebro-basilar arterial diameter in a cisterna megna SAH model in Sprague Dawley rats and intended to explore whether improving early rCBF reduction and cerebral vasospasm could contribute to alleviating blood brain barrier (BBB) dysfunction. In rats for rCBF, vasospasm and BBB permeability assessments, nimodipine (NDP) or saline was administered intravenously 5 minutes after SAH. rCBF within the first 60 minutes after SAH was measured by laser Doppler flowmetry. BBB permeability indexed by Evans Blue extravasation was assessed 4 hours after SAH. Angiography for the caliber changes of the vertebro-basilar artery were conducted 30 minutes post SAH. Pronounced rCBF reduction and vasospasm were observed soon after SAH, followed by BBB permeability increment. NDP administration could improve rCBF and attenuate vasospasm, followed by the alleviation of BBB permeability. Our results demonstrate that early improvement of cerebral circulation by NDP may contribute to the reduction in brain injury indexed by BBB disruption.