Abstract: Objective To explore the value of fractional exhaled nitric oxide(FeNO)in the early diagnosis and assessment of children's asthma. Methods A prospective study was conducted for 130 children with bronchial asthma diagnosed in our department. A total of 90 cases in acute attack stage and 40 cases in remission stage were separately selected as acute stage group and remission stage group. Children in acute stage were subdivided into mild group(n=32), moderate group(n=35)and severe group(n= 23)according to the degree of illness. The levels of FeNO, ratio of peak expiratory flow to predicted value(PEF%), ratio of forced expiratory volume in one second to predicted value(FEV₁%)and immunoglobulin E(IgE)were compared in children in the acute group and remission group, as well as those with different degrees of illness. The correlations between FeNO and PEF%, FEV₁%, IgE were analyzed by Pearson method. Results The levels of FeNO and IgE were(68.30±9.21)ppb and(279.32±78.05)kU/L in the acute group, which were higher than(39.27±5.38)ppb and(185.70±52.36)kU/L, in the remission group. PEF% and FEV₁% were(73.50±9.85)% and(78.53±9.76)%, in the acute group, which were significantly lower than(89.65±6.53)% and(90.12±6.74)%, in the remission group, the differences were statistically significant(P < 0.05). There were significant between-group differences in FeNO, PEF%, FEV₁%, IgE among mild, moderate and severe groups(P < 0.05). Pearson analysis showed that FeNO was negatively correlated with PEF% and FEV₁%(r= -0.827, - 0.793, P < 0.01)and positively correlated with serum IgE(r= 0.780, P < 0.01). Conclusion The abnormal elevation - of FeNO in children with asthma in acute stage is significantly correlated with PEF%, FEV₁% of pulmonary function and serum IgE, which provides an important basis for clinical early diagnosis of asthma and disease assessment.