Objective To study the diagnostic value of fractional exhaled nitric oxide(FeNO)in non-typical bronchial asthma.Methods Ninety-five patients with unknown-cause respiratory symptoms including wheezing,cough and breathlessness were enrolled.FeNO was measured by nitric oxide analyzer.The clinical symptoms and bronchial bronchodilator test were defined as golden standard for asthma diagnosis.The diagnostic value of FeNO was assessed and the optimal operating point of FeNO test was determined by means of the receiver operating characteristic(ROC)curve.Results Among 95 patients,44 cases were diagnosed as asthma,51 cases were diagnosed as non-asthma.The level of FeNO of asthma patients were higher than that of non-asthma patients[(55.2±14.0)nmol/L vs.(18.9±5.2)nmol/L,P＜0.01].A non-linear correlation of FeNO with FEV1％ was revealed in the cases with asthma(r=-0.162,P＞0.05).Area under ROC curve was 0.858.The optimal diagnostic cut off point was 36 nmol/L which was capable of differentiating asthma and non-asthma with sensitivity of 80.2％,specificity of 79.5％,positive predictive value of 85.4％,negative predictive value of 83.3％ and accuracy of 85.9％.Conclusions FeNO test may be helpful in the diagnosis of non-typical asthma with high sensitivity and specificity,which can also improve the diagnostic effectiveness and avoid misdiagnosis,missed diagnosis when combined with lung function test.