Objective: Defective innate immune functions can contribute to chronic rhinosinusitis (RS). Recently, it has been reported that chronic RS patients show impaired function of natural killer (NK) cells. We investigated the role of NK cells in eosinophilic inflammation in an allergic RS mouse model. Methods: Mice sensitized to ovalbumin (OVA) by intraperitoneal injection received nasal challenges with OVA for 5 weeks. NK cell depletion was achieved by intraperitoneal injections of anti-asialo ganglio-N-tetraosylceramide (ASGM1) antibodies 10 days before OVA sensitization and every 5 days thereafter until sacrifice. Sinonasal complex samples were evaluated histologically, and IL-4, IL-5, IL-13, IFN-γ, MIP-2, and eotaxin levels were measured in the nasal lavage fluid. Differential white blood cell counts were also obtained. Results: Allergic RS mice showed significantly more eosinophilic inflammation in the sinonasal mucosa, elevated levels of IL-4, IL-5, IL-13, and eotaxin in the nasal lavage fluid, and peripheral blood eosinophilia compared to control mice. The depletion of NK cells by anti-ASGM1 treatment induced more prominent eosinophilic inflammation and increased secretion of IL-5 and peripheral blood eosinophilia in allergic RS mice. Conclusion: The depletion of NK cells aggravates allergen-induced sinonasal eosinophilic inflammation, suggesting that impaired NK cell activity may be an exacerbating factor in eosinophilic chronic RS.