Abstract: In order to study the therapeutic time window of dimethylaminoethyl ginkgolide B mesylate(XQ-1H) in the permanent focal ischemia of rat，we used the rat model of the permanent middle cerebral artery occlusion（pMCAO）.Doses of 15.6，7.8 and 3.9 mg/kg of XQ-1H were intravenously administered at 0.5，1，2，3 h after MCAO，respectively.Neurological scores，infarct sizes，water contents and pathological changes in each interval were determined at 72 h after MCAO.It was observed that XQ-1H administered at 0.5 and 1 h after MCAO significantly reduced the cerebral infarct size and edema，and produced significant reductions in the neurological deficits.The protective effect of XQ-1H on the neuron cells was proved by pathological observations.In addition，the contents of MDA，lactate，and the activities of SOD were measured. Reduction in the contents of MDA and lactate and enhancement in the activities of SOD were attributed to the pretreatment of XQ-1H at 0.5 and 1 h.Our results showed that the therapeutic time window of XQ-1H extended for up to 1 h after MCAO.