Objective: Seasonal grass pollinosis has recently become a major problem because many people suffer from this allergy. In this study, we evaluate the clinical effects of mometasone for seasonal grass pollinosis, the changes of chemical mediators in nasal lavage fluid, and their correlation with the clinical response. Method: Twenty patients were treated with mometasone from May to August 2009. To assess the clinical response, we focused on the changes of symptoms shown by the allergy diary of each patient. We also investigated the correlation of ECP, VEGF, and eotaxin levels in nasal lavage fluid with the severity of symptoms. Results: There was a significant reduction of the symptom score, medication score, and symptom medication score after administration of mometasone, and also ECP, VEGF, and eotaxin levels showed significant reduction in nasal lavage fluid. We found a significant correlation with VEGF and nasal symptoms. Conclusion: These results may allow us to speculate that mometasone furoate nasal spray is effective for the treatment of patients with seasonal grass pollinosis and also useful to improve QOL of these patients.