Background: Peroxisome proliferator-activated receptor γ (PPAR-γ) has been shown to play an important role in the control of inflammatory responses acting on macrophages, mast cells, T cells, and eosinophils. The present study was aimed at investigating the effects of PPAR-γ agonist on nasal symptoms and eosinophil accumulations in nasal mucosa by using a murine allergic rhinitis model. Furthermore, we examined the expression of PPAR-γ in the nasal mucosa in mice. Methods: BALBac mice were sensitized and challenged intranasally with ovalbumin. Ciglitazone, a PPAR-γ agonist, was administered orally 6 hours before each nasal challenge. Results: Administration of PPAR-γ agonist significantly decreased the number of nasal rubs, nasal histamine responsiveness, serum IgE, IL-5 production from the spleen, and eosinophilic infiltration in the nasal mucosa. Furthermore, PPAR-γ was expressed in eosinophils and epithelial cells in the nasal mucosa by immunohistochemistry. Conclusions: PPAR-γ was expressed in eosinophils and epithelial cells in the nasal mucosa. Also, the oral administration of ciglitazone is effective in upper airway allergic inflammation in mice. © 2009 Japanese Society of Allergology.