Abstract: Objective :To investigate mRNA and protein expression levels of NF-κB and IκBα,DNA-binding activity of NF-κB in ESCC cell lines. Methods :Western blotting was used to determine the protein levels of the subunits of NF-κB,p50 and p65,inhibitor-κBα and p-IκBα in two ESCC cell lines Eca109 and EC9706.Nuclear proteins from the ESCC cell lines were extracted to evaluate the protein levels of p50,p65 and the DNA-binding activity by electrophoretic mobility gel shift assay(EMSA).RT-PCR was used to detect the mRNA of p50,p65 and IκBα. Results :ESCC cell lines constitutively overexpressed p50,p65,IκBα and p-IκBα in the cytoplasm.The proteins of p50 and p65 were also expressed in the nuclei and had high DNA-binding activity.In addition,the results of RT-PCR showed overexpression of p50,p65 and IκBα mRNA. Conclusion :The findings indicate that NF-κB is constitutively activated in human ESCC cell lines,which may be caused by its gene overexpression or the phosphorylation of IκBα,suggesting that NF-κB may play a critical role in carcinogenesis of the esophagus.