Background: The epithelial-mesenchymal transition (EMT) is a distinguishing characteristic of chronic rhinosinusitis with nasal polyps (CRSwNP). The underlying mechanism remains largely unknown. Arachidonate 15-lipoxygenase (ALOX15), an enzyme involved in arachidonic acid metabolism, has been reported to cause airway epithelial injury and thus may further promote the EMT. The aim of this study was to evaluate the role of ALOX15 during the EMT process in CRSwNP. Methods: A total of 54 samples were obtained, including 10 from healthy control, 16 from non-eosinophilic CRSwNP, and 28 from eosinophilic CRSwNP. Hematoxylin and eosin staining was performed to determine the basement membrane (BM) thickness. The concentration of molecules mediating remodeling was assayed by Luminex. The messenger RNA (mRNA) and protein levels of target genes were measured by quantitative real-time polymerase chain reaction (PCR) and Western blotting. Results: EMT was enhanced in eosinophilic CRSwNP compared with the healthy controls and non-eosinophilic CRSwNP infiltrated with lymphocytes and/or plasma cells. The expression pattern of molecules related to remodeling, including matrix metalloproteinases (MMPs), tissue inhibitor of metalloproteinases (TIMPs), and transforming growth factor beta (TGF-beta) family members, differed between the subtypes of CRSwNP. The mRNA level of ALOX15 was correlated with the BM thickness and MMP-1 and TGF-beta 3 expression. The inhibition of ALOX15 by PD146176 could induce claudin-1, claudin-4, claudin-7, zonula occludens (ZO)-1, ZO-2, E-Cadherin, TIMP-1, and TIMP-3 expressions and reduce the levels of MMP-1 and N-Cadherin in epithelial cells acquired from eosinophilic CRSwNP patients. Conclusion: The specific inhibition of ALOX15 could attenuate the EMT, which may provide an alternative method for the treatment of CRSwNP. (C) 2018 ARS-AAOA, LLC.