Background: Asthma is a chronic inflammatory disease of multifactorial etiologies. The eosinophil is a major player in allergic disease. Therefore, direct measurement of eosinophilic inflammation is needed for diagnosis. Objective: To assess Eosinophil-Derived Neurotoxin serum level in children with bronchial asthma. Also, to determine the relation of these levels to severity of bronchial asthma in children. Patients and methods: This case control prospective study was conducted during the period from August 2018 to August 2019. This study included 85 cases (17 in each group) divided into: control, intermittent, mild, moderate and severe persistent asthma groups. This study was carried out at Pediatric Department of Zagazig University Hospitals. Results: Eosinophil-Derived Neurotoxin (EDN) concentrations were significantly increased in asthmatic children when compared to controls (p-value < 0.05). The current work revealed that EDN levels can be considered as a possible biomarker for asthma diagnosis (PPV = 91.9%, NPV = 100%, sensitivity = 100%, specificity = 64.7%). The level of serum EDN was statistically higher in moderate and severe 0.832. Conclusion: EDN level was higher in asthmatic children than controls and correlated with asthma severity. Therefore, serum EDN can be considered as a possible biomarker for diagnosis, grading of asthma severity and the degree of airway inflammation. Serum EDN had a significant correlation with mean spirometric parameters in asthmatics. Therefore, it can reflect airway resistance in asthmatic children.