Abstract: Objective：To evaluate the diagnostic value of fractional exhaled nitric oxide (FeNO) in allergic asthma. Methods：A total of 147 cases of asthma patients who were newly diagnosed or non-standardly treated in the Respiratory Department of Zhongshan Hospital Affiliated to Fudan University from August 2015 to September 2016 were enrolled. The patients were divided into allergic asthma group (n=107) and non-allergic asthma group (n=40). Before standardized treatment, FeNO, lung function, and serum total IgE tests were performed. The receiver operating characteristic curve (ROC) was made to evaluate the diagnostic value of FeNO in allergic asthma. Results：The values of FeNO and total serum IgE were significantly higher in allergic asthma group than those in non-allergic asthma group (P<0.05), but there was no statistical difference between these two groups in FEV1%pred, FEV1/FVC, or FVC%pred. In allergic asthma group, the FeNO level was positively correlated with serum total IgE (r=0.298, P<0.001), but had no correlation with FEV1%pred, FEV1/FVC, or FVC%pred. There was no correlation between FeNO and serum total IgE, FEV1%, FEV1/FVC, or FVC% in non-allergic asthma group. Further, the allergic group were divided to two groups according the bronchial dilation test and no statistical difference in FeNO was found between these two groups. In allergic asthma group, there was no statistical difference in FeNO levels between positive and negative patients in the bronchial dilation test. The cut-off value of FeNO to differentiate allergic asthma was 40.05 ppb (1 ppb=1 μL/m3) according to the ROC curve (AUC 0.971, sensitivity 96.3%, specificity 85.0%). Conclusions：FeNO is significantly increased in newly diagnosed or non-standard treatment of allergic asthma and has positive correlation with serum total IgE. When the FeNO value is above 40.05 ppb, the diagnosis of allergic asthma is highly likely. Thus, FeNO is an important and objective indicator in the diagnosis of allergic asthma.