objective:to explore the diagnostic value of the fractional exhaled nitric oxide(feno) for asthma in children. methods:the patients with unkown-caused respiratory symptoms including wheezing, cough and breathlessness were enrolled from jun to sep in 2010. feno was measured by nitric oxide analyzer. bronchial challenge test and bronchodilator test were defined as golden standard for asthma diagnosis in children. the diagnostic value of feno was assessed and the optimal operating point of feno testing was determined by the means of the receiver operating characteristic(roc) curve. results:a total of 87 patients were enrolled, in which 52 cases were diagnosed as asthma by positive result in bronchial challenge test or bronchodilator test, and the other 35 cases were non-asthma. the level of feno in asthma group was higher than non-asthma group[(59.77±42.48)ppb vs(25.26±22.60)ppb, p < 0.05]. the level of feno was correlated with the counts of eosinophile granulocyte(r=0.546,p < 0.01) but not correlated with fev1%(r=-0.151,p > 0.05). area under roc curve was 0.818. the optimal diagnostic cut-off point was 34.5 ppb which was capable of differentiating asthma and non-asthma with sensitivity of 0.712, specificity of 0.686, positive predictive value of 0.755, negative predictive value of 0.605 and accuracy of 0.689. conclusion:determination fo feno may be helpful in the diagnosis of asthma in children.