Abstract： This study is to investigate the effect of hydroxyethylpuerarin on the expression of tumor necrosis factor-alpha (TNF-α) and activity of nuclear factor kappa B (NF-κB) after middle cerebral artery occlusion (MCAO) in rats. Rats were subjected to cerebral ischemia-reperfusion injury induced by MCAO. Hydroxyethylpuerarin (10, 20, 40 mg·kg-1, iv) was administered just 30 min before occlusion and immediately after reperfusion. After a 24 h reperfusion following 2 h of MCAO, the number of viable neurons in hippocampal CA1 region was counted by hematoxylin and eosin (HE) staining. TNF-α protein and its mRNA expression were examined with radioimmunoassay (RIA) and reverse transcriptase-polymerase chain reaction (RT-PCR) respectively. NF-κB activity was observed by electrophoretic mobility shift assay (EMSA), and inhibition of NF-κB α (IκBα) protein expression was evaluated by Western blotting analysis. Animals treated with hydroxyethylpuerarin had a significant increase in neuronal survival in comparison with vehicle-treated group. Hydroxyethylpuerarin significantly reduced the protein and mRNA expression of TNF-α following 2 h of ischemia with 24 h of reperfusion. NF-κB DNA binding activity and the degradation of IκBα in the cytoplasm also decreased by hydroxyethylpuerarin treatment. The protective effects of hydroxyethylpuerarin against ischemia-reperfusion injury may be mediated by decreasing the expression of TNF-α and the activity of NF-κB in rats.