The epithelial-mesenchymal transition (EMT) has been recognized to occur during embryonic development, fibrosis, and tumor metastasis. Nuclear factor (NF)-κB plays a central role in mediating the inflammation and wound-healing responses during liver fibrogenesis. However, the involvement of NF-κB during EMT in liver cells remains unidentified. To develop a therapeutic approach to EMT during liver fibrosis, we examined the inhibition of transcription factor NF-κB, using a decoy oligodeoxynucleotide (ODN) strategy in liver fibrosis in vitro and in vivo. NF-κB decoy ODN contains consensus binding sequences of the NF-κB-binding site. NF-κB decoy ODN effectively suppresses transforming growth factor-β(1)-induced EMT in AML12 murine hepatocytes. Liver fibrosis induced by CCl(4) administration was suppressed by NF-κB decoy ODN. Furthermore, NF-κB decoy ODN was shown to inhibit the EMT process in fibrotic liver in vivo. This study demonstrates the feasibility of NF-κB decoy ODN treatment for preventing liver fibrosis via EMT processes.