Background Eosinophilic chronic rhinitis with nasal polyps (eos-CRSwNP) is a subtype of nasal polyps (NPs) characterized by severe type-2 inflammation and defective epithelial barrier function. The epithelial barrier plays important roles in the pathogenesis of NPs and type-2 inflammation. Particular matter 2.5 (PM2.5) are fine particles with a diameter less than 2.5 mu m, containing a mixture of different components. Here, we investigated the impact of PM2.5 on the barrier function of the eos-CRSwNP epithelium and explored the reparative function of budesonide. Methods Samples from noninflammatory nasal mucosa and eos-CRSwNP were collected to establish an in vitro air-liquid interface cultured model. The cells were exposed to PM2.5 at 50 or 100 mu g/ml intermittently for 72 h, with or without budesonide pretreatment. Barrier function and tight junction (TJ) expression were reflected by measuring transepithelial resistance (TER), paracellular flux permeability of fluorescein isothiocyanate-labeled 4-kDa dextran, quantitative real-time polymerase chain reaction (qPCR), and immunofluorescence staining of TJ proteins. Cytokine expression was measured by qPCR and enzyme-linked immunosorbent assay or Luminex. Results PM2.5 increased paracellular flux and downregulated TJ protein expression (zona occuldens-1, occludin, and claudin-1), but did not change TER. These changes could be partially restored by budesonide treatment. Interleukin (IL)-8, IL-10, IL-1 alpha, and tissue inhibitor of metalloproteinase (TIMP)-1 concentrations were significantly increased in the culture medium of cells exposed to PM2.5, and budesonide significantly reduced the changes in IL-8, IL-1 alpha, and TIMP-1. Conclusion PM2.5 impaired the barrier function of eos-CRSwNP epithelial cells and increased the permeability of large molecules. PM2.5 also increased the secretion of pro-inflammatory cytokines by nasal epithelial cells. Budesonide could partially repair the damage, suggesting potential applications in clinical practice.