Aim To investigate the effect of Buyang Huanwu Decoction on blood-brain barrier of cerebral ischemia and reperfusion rats,and explore the mechenism of the decoction.Methods 48 normal male SD rats were distributed randomLy to 3 groups: ①Sham-operation(n=16);②Control(n=16);③Buyang Huanwu Decoction(n=16).Cerebral ischemia and reperfusion rat models were made using the method of thread inserting right middle cerebral artery occlusion(MCAO),The brain water content were measured 48 h after reperfusion.At the same time,The permeability of blood-brain barrier was observed with electron microscope and by detecting the content of Evans Blue leaked out the brain tissue of ischemic side.The expression of MMP-9 in different groups was detected by Western Blotting,The transcription of MMP-9 mRNA was detected by RT-PCR.Results 48 h After crebral ischemia and reperfusion injuries,the content of brain water and Evans Blue leaked out the brain tissue of ischemic side increased obviously,The breakdown of blood-brain barrier was severe on electron microscope,the transcription and expression of MMP-9 also increased obviously.However,Buyang Huanwu Decoction can subtract the content of brain edema(p<0.05) and Evans blue(p<0.01),relieve the breakdowm of blood-brain barrier on electron microscope.The transcription and expression of MMP9 were decreased in BYHWD group contrasted with control group(p<0.05).Conclusion BYHWD has the protective effect on BBB in the model rats of cerebral ischemia and reperfusion injuries.The mechanism may be by restrainning the expression and transcription of MMP-9.