Objective: To investigate the clinical significance of dynamic changes of nasal exhaled nitric oxide (FnNO) in the treatment of chronic sinusitis (CRS) in children. Methods: 933 results of FnNO in Shenzhen Children’s Hospital from 2018 to 2020 were reviewed.20 hospitalized children with chronic sinusitis who were followed up for FnNO changes were included.According to the history of allergic diseases, the patients were divided into CRS with allergy group (n = 10) and CRS without allergy group (n = 10).The level of FnNO was measured by the Sunvou exhaled NO measuring system and the passive exhalation and silence technique. Results: 20 children had chronic cough longer than 3 months, 16 children had nasal congestion, and 10 children had a history of allergy.After 36 months of follow-up, the average FnNO of 20 children with chronic sinusitis was 89ppb.The difference of FnNO in 20 children before and after treatment was statistically significant (150±164) ppb VS (337±280) ppb, P<0.05.FnNO in the group with allergy increased significantly after treatment compared with before(136±116) ppb VS (519±280)ppb, P<0.01.There was no significant difference in the group without allergy before and after treatment (164±206)ppb VS (156±120)ppb, P>0.05.The clinical data of 10 patients with CRS without allergy group were reviewed. FnNO level of 4 patients continued to decrease without significant improvement, 3 of them were diagnosed with PCD and FnNO<77ppb after repeated reexamination.Cystic fibrosis (CF) was confirmed in 1 case. Conclusion：The FnNO level is often significantly reduced in children chronic sinusitis which may be related to allergy or nasal obstruction.FnNO level gradually tended to normal after regular treatment in children chronic sinusitis.The FnNO level continuously decreased in children who with chronic sinusitis should be alert to whether they are complicated with basic diseases,such as PCD or CF. [KEY WORDS] Nasal nitric oxide; Chronic sinusitis; Children; Allergy; Primary ciliary dyskinesia