Background: NF-kB comprises a family of transcription factors that are involved in regulating large number of genes related to immune function, inflammation, apoptosis and cell proliferation. PS-341 (noble synthetic NF-kB inhibitor) inhibits 26S proteosome induced IkB degradation and suppresses NF-kB activation. We examined the effect of PS-431 on neointimal formation after rat carotid balloon injury. Methods: PS-341(0.2mg/kg) was systemically administered from the 3rd day after the carotid balloon denudation until 2 weeks via tail vein. We compared the degree of neointimal formation on carotid artery and tissue expression pattern of NF-kB/ IkB in both groups on 14th day after the balloon injury (n=10/group). Results: 1) PS-341 treatment group showed significant reduction of neointimal formation compared with control (p<0.05). 2) Also, PS-341 significantly decreased intima/media (I/M) ratio (control vs PS-341, 1.68 짹 0.29 vs 1.05 짹 0.28, p<0.05). 3) In western blot analysis, the expression patterns of Ik-B were increased in treatment group and ratio of NF-kB/IkB was also decreased in treatment group. 4) Whereas, NF-kB expression patterns were similar in both groups. Conclusion: These results suggested that NF-kB system plays an important role in neointimal formation after balloon injury. Specific and more potent NF-kB inhibitors may be used to prevent restenosis after balloon angioplasty.