Objective：To explore the effects of different doses of dexmedetomidine（DEX）preconditioning on focal in cerebral ischemia reperfusion injury rats. Methods：Fifty healthy male Sprague-Dawley rats were randomly divided into the sham operation group（sham group），the ischemia-reperfusion group（I/R group），the low-dose dexmedetomidine group（D1 group），the medium-dose dexmedetomidine group（D2 group），and the larger-dose dexmedetomidine group（D3 group）. The sham group received surgical procedures without causing ischemia. The sham group and the I/R group received 1 mL normal saline intraperitoneally 30 minutes before ischemia，and the D1，D2 and D3 groups were injected with dexmedetomidine in 50 μg/kg，100 μg/kg and 200 μg/kg，respectively. The levels of S100β protein were measured 24 h and 48 h after reperfusion，the contents of Bcl-2，Bax and the volume of cerebral infarction were determined 48 h after reperfusion. Results：Compared with the I/R group，the protein contents of S100β，Bax，and the volume of cerebral infarction in the D1，D2 and D3 groups were lower（P＜0.05），but were higher than those in the sham group（P＜0.05）；the Bcl-2 expression were increased（P＜0.05），but were lower than that in the sham group（P＜0.05）. The content of Bcl-2 was lower and the content of S100β protein at 24 h after surgery was higher in the D3 group than that in the D1 and D2 groups（P＜0.05），but were not statistically different between the D1 and D2 groups. The expression level of protein S100β，Bax and the volume of cerebral infarction were not statistically different between the D1，D2 and D3 groups. Conclusion：Dexmedetomidine preconditioning has neuroprotective effect on focal cerebral ischemia reperfusion injury in rats，and the mechanism may be related to the inhibition of apoptosis. The effect of dexmedetomidine has no significant difference between 50 μg/kg and 100 μg/kg.