Background: Cigarette smoke (CS) induces lung infiammation and simultaneously activates anti-oxidative pathway as a defense mechanism. Recently, we found that neutrophil elastase (NE) enhances cigarette smoke extract (CSE)-induced infiammation. Therefore, this study was undertaken to investigate the roles of NE on CSE-induced activation of anti-oxidative pathway and its regulatory mechanism in normal human bronchial epithelial cells. Methods: BEAS-2B cells were used. Nrf2 activity assay using nuclear extracts was performed. The expression of heme oxygenase-1 (HO-1) or nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA was determined by real-time PCR. HO-1, Nrf2, DJ-1, or KEAP1 protein expressions were analyzed by Western blotting. Results: CSE activated Nrf2, a transcription factor, which regulates the expression of several antioxidants. CSE increased anti-oxidant, HO-1. Interestingly, NE suppressed CSE-induced expression of HO-1 mRNA and protein. Therefore, we first evaluated the effect of NE on Nrf2. Although NE did not affect the basal and inducible level of Nrf2 mRNA, it significantly decreased the expression of Nrf2 protein. Nrf2 protein stability has been reported to be regulated by DJ-1 and KEAP1. However, the expression level of DJ-1 and KEAP1 did not change in NE-treated cells. Nrf2 down-regulation by NE was not blocked by pre-treatment with proteasomal & lysosomal inhibitors (MG132, PS-341 & chloroquine, NH4Cl), pan-caspase inhibitor (zVAD-fmk), or ROS blocker (NAC). Conclusions: Taken together, these data suggest that NE accelerates CSE-induced damage in lung epithelial cells by blocking anti-oxidative pathway via down-regulation of Nrf2 at the post-translational step.