Objective To investigate the effects of PJ34,a poly ADP-ribose polymerase(PARP)inhibitor,on the expression of matrix metallopro-teinases-9( MMP-9 )and Claudin-5 in ischemic cortex of rats with focal cerebral ischemia-reperfusion(I/R)injury. Methods The focal cerebral ischemia-reperfusion model of middle cerebral artery occlusion(MCAO)was established by intraluminal suture . PJ34 was injected intraperitoneal-ly. Blood-brain barrier(BBB)permeability was quantitatively determined by Evans blue assay. Infarct volume changes were observed by 2,3,5-tri-phenyltetrazolium chloridedyeing(TTC)staining. The expression of the MMP-9 and Claudin-5 in rats of cerebral cortex were measured by immuno-histochemistry assay and western blot analysis . Results Compared with sham group,the expression of MMP-9,the contents of EB and infarct vol-ume increased progressively over time after I/R,and reached maximum levels at 48 h(P<0.05);The expression of Claudin-5,the contents of EB and infarct volume reduced significantly over time after I/R,and reached the minimum levels at 48 h in model group(P<0.05). Compared with model group,the expression of MMP-9,the contents of EB and infarct volume was reduced significantly and the expression of Claudin-5,the con-tents of EB and infarct volume was increased at the same time point in PJ34 group(P<0.05). Conclusion PJ34 maintained the blood-brain barri-er permeability by inhibiting the expression of MMP-9,and increasing the expression of Claudin-5,which had neuroprotection on cerebral ischemia-reperfusion injury.