Abstract： A preliminary study from our research group showed that picroside II inhibited neuronal apop-tosis in ischemic penumbra, reduced ischemic volume, and improved neurobehavioral function in rats with cerebral ischemia. The aim of the present study was to validate the neuroprotective effects of picroside II and optimize its therapeutic time window and dose in a rat model of ce-rebral ischemia. We found that picroside II inhibited cell apoptosis and reduced the expression of neuron-speciifc enolase, a marker of neuronal damage, in rats after cerebral ischemic injury. The optimal treatment time after ischemic injury and dose were determined, respectively, as fol-lows:(1) 2.0 hours and 10 mg/kg according to the results of toluidine blue staining;(2) 1.5 hours and 10 mg/kg according to early apoptotic ratio by lfow cytometry;(3) 2.0 hours and 10 mg/kg according to immunohistochemical and western blot analysis;and (4) 1.5 hours and 10 mg/kg according to reverse transcription polymerase chain reaction. The present ifndings suggest that an intraperitoneal injection of 10 mg/kg picroside II 1.5-2.0 hours after cerebral ischemic injury in rats is the optimal dose and time for therapeutic beneift.