Background: Bronchial asthma is chronic inflammatory disease of the respiratory tract, in which many cells of innate and adaptive immune system in combination with epithelial cells are involved causing the main clinical typical criteria for the disease. Osteopontin (OPN) is identified in many cell types in the immune system. OPN is a protein expressed during the inflammatory processes related to Th2 lymphocyte activity. Objective: The aim of the current study was to evaluate serum osteopontin level as biomarker in the diagnosis of bronchial asthma in different age groups. Patients and Methods: This prospective case-control study was carried out at the Pediatric Department, Zagazig University Hospitals from May 2019 till December 2019. All patients were subjected to full history taking and laboratory investigations including measurement of Human Osteopontin (OPN). Results: There was high significant positive correlation between osteopontin and S. IgE and AEC. Also, there was high significant negative correlation between osteopontin and forced expiratory volume 1 (FEV1), forced vital capacity (FVC) and peak expiratory flow (PEF) in both age groups. There was significant difference between <5 years severe asthma and 5-12 years severe asthma as regard Osteopontin level. Conclusion: It could be concluded that there is strong association between OPN concentration and disease severity. OPN shows high significant difference between asthmatic and control group. Serum OPN is a good biomarker in the diagnosis of bronchial asthma at different age groups.