The proprotein convertases are serine proteases responsible for the proteolytic maturation of many precursor proteins involved in upper airway remodeling during nasal polyposis. We have previously found that proprotein convertase PC1/3 is expressed in human nasal mucosa. However, whether PC1/3 is related to nasal polyp formation has not been investigated. To gain insight into the functional role of PC1/3 in nasal polyps, we determined PC1/3 expression in nasal polyps by immunostaining, western blotting, and enzyme assays and generated stable cells expressing PC1/3 using airway epithelial cell line NCI-H292. Nasal polyps exhibit increased PC1/3 expression compared to normal nasal mucosa. PC1/3 was expressed in neuroendocrine cells in normal nasal mucosa and it was also expressed in goblet and ciliated cells in nasal polyps. NCI-H292 cells stably expressing PC1/3 displayed morphological changes, enhanced cell proliferation and migration, down-regulation of E-cadherin and cytokeratins and up-regulation of N-cadherin, vimentin, matrix metalloproteinase-2, collagen-I, Snail, and Twist. Importantly, PC1/3 expression was positively correlated with epithelial-mesenchymal transition in cultured human nasal epithelial cells and in nasal polyps. Taken together, our data suggest that PC1/3 overexpression induces morphological and phenotypic epithelial-mesenchymal transition changes of airway epithelial cells and these changes may contribute to the pathogenesis of nasal polyps.