Background: Recurrent wheezing is a common condition in pediatric practice, with estimates that one in three children develop at least one episode of wheezing prior to their third birthday. Objective: to assess the diagnostic and prognostic value of serum eosinophil derived neurotoxin (EDN) levels in children with asthma and preschool wheezes (PSW) in relation to their clinical and laboratory parameters. Methods: This is a cross-sectional studyconducted on a stratified random sample of 60 patients, following up in Pediatric Allergy, Immunology and Rheumatology unit, Children's hospital, Ain Shams university. Patients were compared to age and sex 30 healthy controls. EDN was analyzed using ELISA in the Clinical Pathology Immunology Laboratory, Ain Shams university Hospitals, in the period between June 2022 to November 2022. Results: There was statistically significant increase in relative eosinophil percentage (P value<0.001), absolute eosinophil count (P value<0.001) and EDN (P value<0.001) among the cases group compared with the controls. Serum EDN was significantly higher in patients with asthma and patients with PSW than in controls. For prediction of allergic respiratory diseases (asthmatic and school wheezers), the best cutoff value is > 7.8 with sensitivity =100% and specificity =96.67%. Conclusion: EDN is a good biomarker for eosinophilic inflammation in pediatric asthma and PSW with an excellent diagnostic and prognostic value. Therefore, EDN can be used as a screening tool to identify the phenotype of respiratory allergy. Further studies are needed to outline its therapeutic potentials.