Cumulative evidence has indicated a critical role of poly(ADP-ribose) polymerase-1 activation in ischemic brain damage. Poly(ADP-ribose) glycohydrolase (PARG) is a key enzyme in poly(ADP-ribose) catabolism. Our previous studies showed that PARG inhibitors, gallotannin (GT) and nobotanin B, can profoundly decrease oxidative cell death in vitro. Here, we tested the hypothesis that intranasal delivery of GT can decrease ischemic brain damage by inhibiting PARG. Intranasal delivery of GT within 5 hours after the onset of focal brain ischemia markedly decreased the infarct formation and neurological deficits of rats. The GT administration also increased poly(ADP-ribose) in the ischemic brains, suggesting that GT acts as a PARG inhibitor in vivo. Furthermore, the GT treatment abolished nuclear translocation of apoptosis-inducing factor (AIF) in the ischemic brains, suggesting that prevention of AIF translocation may contribute to the protective effects of GT. In contrast, intravenous injection of GT, at 2 hours after ischemic onset, did not reduce ischemic brain damage. Collectively, our findings suggest that PARG inhibition can significantly decrease ischemic brain injury, possibly by blocking AIF translocation. This study also highlights distinct merits of intranasal drug delivery for treating CNS diseases.