Objective · To explore the effect of endoplasmic reticulum stress (ERS) on neutrophil elastase (NE) induced mucin 5AC (MUC5AC) production in human airway epithelial cells. Methods · HBE16 airway epithelial cells were cultured and pretreated with reactive oxygen species (ROS) inhibitor N-acetylcysteine (NAC) or ERS inhibitor 4-phenylbutyrate (4-PBA), or transfected with small interfering RNA (siRNA) against inositolrequiring kinase 1α (IRE-1α) or X-box binding protein 1 (XBP-1), respectively before incubation with NE. NE group and blank control group were also set up. ROS production was assayeddetection kit; of glucose-regulated protein 78 (GRP78), phosphorylated protein kinase R-like endoplasmic reticulum kinase (pPERK), activating transcription factor 6 (ATF6), phosphorylated IRE-1α (pIRE-1α), and XBP-1 protein was detectedWestern blotting; spliced XBP-1 (XBP-1s) mRNA was measuredreal-time PCR; levels of MUC5AC protein in culture supernatant and cytoplasm were assayedELISA and immunofluorescence. Results · There was an obvious increase of ROS production with strong elevation of GRP78, ATF6, pPERK, and pIRE-1α protein in NE group cells after 24 h, compared with blank control group (P<0.05). The protein and mRNA of XBP-1s, and MUC5AC production also increased obviously (P<0.05). NAC and 4-PBA reduced ERS-related protein and MUC5AC production and secretion (P<0.05). Further studies showed that MUC5AC secretion was also bluntedIRE-1α siRNA or XBP-1 siRNA, accompanied with decreased of XBP-1s mRNA and protein (P<0.05). Conclusion · NE induces ERSproducing ROS, and increases MUC5AC protein production and secretion; IRE-1α/XBP-1 play a certain role in this process.