Background: In allergic inflammation, the cells existing in the mucosa take up antigens and present them to produce specific IgE, but there is no clinical study that quantifies antigens that cause allergies in local tissues. Fungi can induce the formation of nasal polyps via epithelial damage and type-2 inflammation. Aspergillus fumigatus is the most common environmental allergen; however, the involvement of its specific antigens in local allergic reactions in nasal polyps has not yet been reported. Objective: To investigate local allergic reactions to the Aspergillus fumigatus antigen, Asp f 1 in patients with CRSwNP. Materials and Methods: Nasal polyp tissues were collected from 103 patients with CRSwNP during surgery and homogenized. Tissue eosinophil counts and Asp f1, Aspergillus-specific IgE, type 2 cytokines and galectin-10 levels were measured in nasal polyps. Results: Eighteen cases (15.9%) of 103 patients were positive for Asp f 1 and were divided into two groups based on Asp f 1 levels. Asp f 1 levels positively correlated with Aspergillus-specific IgE levels (r =0.68, p <0.01). Aspergillus-specific IgE (p <0.01) levels in nasal polyps were significantly higher in the high Asp f 1 group than in the low Asp f 1 group although no significant differences were observed in IgM levels between these groups. Furthermore, Asp f 1 levels positively correlated with tissue IL-4 levels (r =0.85, p <0.0005) or tissue galectin-10 levels (r =0.54, p<0.01). Conclusion: This is the first study to quantify the levels of Aspergillus fumigatus antigen in the nasal polyps of patients with CRSwNP. The presence of Asp f 1 might explain the local type 2 allergic reaction to Aspergillus fumigatus in CRSwNP.