Abstract: Dimethylaminoethyl ginkgolide B mesylate（XQ-1H）therapeutic time window in rat focal cerebral ischemia was investigated using rat model of middle cerebral artery occlusion（MCAO,induced by intraluminal suture method).Following MCAO,different doses of XQ-1H were administered（ig）at 1,2 and 3 h,respectively. Regional cerebral blood flow,neurological score,infarction rate,water content and pathological change of rats at each interval were determined 24 h after MCAO.It was observed that the regional cerebral blood flow was increased and neurological score,cerebral infarction rate and water content were reduced significantly at 1 h,2 h（XQ-1H administered after MCAO）.The results showed that the neuroprotective effect of XQ-1H on the therapeutic window in focal cerebral ischemia injury of rats was extended to 2 h.