Sanguisorbae radix (SR), the root of Sanguisorba officinalis L. (Rosaceae), has been traditionally used for its anti-inflammatory, anti-infectious and analgesic activities in Korea. Previous work has shown that SR prevents neuronal cell damage induced by Aβ (25—35) in cultured rat cortical neurons. The present study was carried out to further investigate the neuroprotective effect of SR on oxidative stress-induced toxicity in primary culture of rat cortical neurons, and on ischemia-induced brain damage in rats. SR, over a concentration range of 10—50 μg/ml, inhibited H₂O₂ (100 μM)-induced neuronal death, which was significantly inhibited by MK-801 (5 μM), an N-methyl-D-aspartate (NMDA) receptor antagonist, and verapamil (20 μM), an L-type Ca²⁺ channel blocker. Pretreatment of SR (10—50 μg/ml), MK-801 (5 μM), and verapamil (20 μM) inhibited H₂O₂-induced elevation of intracellular Ca²⁺ concentration ([Ca²⁺]_i) measured by a fluorescent dye, Fluo-4 AM. SR (10—50 μg/ml) inhibited H₂O₂-induced glutamate release into medium measured by HPLC, and generation of reactive oxygen species (ROS) measured by 2′,7′-dichlorodihydrofluorescein diacetate (H₂DCFDA). In vivo, SR prevented cerebral ischemic injury induced by 2-h middle cerebral artery occlusion (MCAO) and 24-h reperfusion. The ischemic infarct and edema were significantly reduced in rats that received SR (10, 30 mg/kg, orally), with a corresponding improvement in neurological function. Catechin isolated from SR inhibited H₂O₂-induced neuronal death in cultures. Taken together, these results suggest that SR inhibits H₂O₂-induced neuronal death by interfering with the increase of [Ca²⁺]_i, and inhibiting glutamate release and generation of ROS, and that the neuroprotective effect of SR against focal cerebral ischemic injury is due to its anti-oxidative effects. Thus SR might have therapeutic roles in neurodegenerative diseases such as stroke.